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Python 3.6.5 Documentation > "datetime" — Basic date and time types

"datetime" — Basic date and time types
**************************************

**Source code:** Lib/datetime.py

======================================================================

The "datetime" module supplies classes for manipulating dates and
times in both simple and complex ways. While date and time arithmetic
is supported, the focus of the implementation is on efficient
attribute extraction for output formatting and manipulation. For
related functionality, see also the "time" and "calendar" modules.

There are two kinds of date and time objects: “naive” and “aware”.

An aware object has sufficient knowledge of applicable algorithmic and
political time adjustments, such as time zone and daylight saving time
information, to locate itself relative to other aware objects. An
aware object is used to represent a specific moment in time that is
not open to interpretation [1].

A naive object does not contain enough information to unambiguously
locate itself relative to other date/time objects. Whether a naive
object represents Coordinated Universal Time (UTC), local time, or
time in some other timezone is purely up to the program, just like it
is up to the program whether a particular number represents metres,
miles, or mass. Naive objects are easy to understand and to work
with, at the cost of ignoring some aspects of reality.

For applications requiring aware objects, "datetime" and "time"
objects have an optional time zone information attribute, "tzinfo",
that can be set to an instance of a subclass of the abstract "tzinfo"
class. These "tzinfo" objects capture information about the offset
from UTC time, the time zone name, and whether Daylight Saving Time is
in effect. Note that only one concrete "tzinfo" class, the "timezone"
class, is supplied by the "datetime" module. The "timezone" class can
represent simple timezones with fixed offset from UTC, such as UTC
itself or North American EST and EDT timezones. Supporting timezones
at deeper levels of detail is up to the application. The rules for
time adjustment across the world are more political than rational,
change frequently, and there is no standard suitable for every
application aside from UTC.

The "datetime" module exports the following constants:

datetime.MINYEAR

The smallest year number allowed in a "date" or "datetime" object.
"MINYEAR" is "1".

datetime.MAXYEAR

The largest year number allowed in a "date" or "datetime" object.
"MAXYEAR" is "9999".

See also:

Module "calendar"
General calendar related functions.

Module "time"
Time access and conversions.

Available Types
===============

class datetime.date

An idealized naive date, assuming the current Gregorian calendar
always was, and always will be, in effect. Attributes: "year",
"month", and "day".

class datetime.time

An idealized time, independent of any particular day, assuming that
every day has exactly 24*60*60 seconds (there is no notion of “leap
seconds” here). Attributes: "hour", "minute", "second",
"microsecond", and "tzinfo".

class datetime.datetime

A combination of a date and a time. Attributes: "year", "month",
"day", "hour", "minute", "second", "microsecond", and "tzinfo".

class datetime.timedelta

A duration expressing the difference between two "date", "time", or
"datetime" instances to microsecond resolution.

class datetime.tzinfo

An abstract base class for time zone information objects. These
are used by the "datetime" and "time" classes to provide a
customizable notion of time adjustment (for example, to account for
time zone and/or daylight saving time).

class datetime.timezone

A class that implements the "tzinfo" abstract base class as a fixed
offset from the UTC.

New in version 3.2.

Objects of these types are immutable.

Objects of the "date" type are always naive.

An object of type "time" or "datetime" may be naive or aware. A
"datetime" object *d* is aware if "d.tzinfo" is not "None" and
"d.tzinfo.utcoffset(d)" does not return "None". If "d.tzinfo" is
"None", or if "d.tzinfo" is not "None" but "d.tzinfo.utcoffset(d)"
returns "None", *d* is naive. A "time" object *t* is aware if
"t.tzinfo" is not "None" and "t.tzinfo.utcoffset(None)" does not
return "None". Otherwise, *t* is naive.

The distinction between naive and aware doesn’t apply to "timedelta"
objects.

Subclass relationships:

object
timedelta
tzinfo
timezone
time
date
datetime

"timedelta" Objects
===================

A "timedelta" object represents a duration, the difference between two
dates or times.

class datetime.timedelta(days=0, seconds=0, microseconds=0, milliseconds=0, minutes=0, hours=0, weeks=0)

All arguments are optional and default to "0". Arguments may be
integers or floats, and may be positive or negative.

Only *days*, *seconds* and *microseconds* are stored internally.
Arguments are converted to those units:

* A millisecond is converted to 1000 microseconds.

* A minute is converted to 60 seconds.

* An hour is converted to 3600 seconds.

* A week is converted to 7 days.

and days, seconds and microseconds are then normalized so that the
representation is unique, with

* "0 <= microseconds < 1000000"

* "0 <= seconds < 3600*24" (the number of seconds in one day)

* "-999999999 <= days <= 999999999"

If any argument is a float and there are fractional microseconds,
the fractional microseconds left over from all arguments are
combined and their sum is rounded to the nearest microsecond using
round-half-to-even tiebreaker. If no argument is a float, the
conversion and normalization processes are exact (no information is
lost).

If the normalized value of days lies outside the indicated range,
"OverflowError" is raised.

Note that normalization of negative values may be surprising at
first. For example,

>>> from datetime import timedelta
>>> d = timedelta(microseconds=-1)
>>> (d.days, d.seconds, d.microseconds)
(-1, 86399, 999999)

Class attributes are:

timedelta.min

The most negative "timedelta" object, "timedelta(-999999999)".

timedelta.max

The most positive "timedelta" object, "timedelta(days=999999999,
hours=23, minutes=59, seconds=59, microseconds=999999)".

timedelta.resolution

The smallest possible difference between non-equal "timedelta"
objects, "timedelta(microseconds=1)".

Note that, because of normalization, "timedelta.max" >
"-timedelta.min". "-timedelta.max" is not representable as a
"timedelta" object.

Instance attributes (read-only):

Supported operations:

+----------------------------------+-------------------------------------------------+
| Operation | Result |
+==================================+=================================================+
| "t1 = t2 + t3" | Sum of *t2* and *t3*. Afterwards *t1*-*t2* == |
| | *t3* and *t1*-*t3* == *t2* are true. (1) |
+----------------------------------+-------------------------------------------------+
| "t1 = t2 - t3" | Difference of *t2* and *t3*. Afterwards *t1* == |
| | *t2* - *t3* and *t2* == *t1* + *t3* are true. |
| | (1) |
+----------------------------------+-------------------------------------------------+
| "t1 = t2 * i or t1 = i * t2" | Delta multiplied by an integer. Afterwards *t1* |
| | // i == *t2* is true, provided "i != 0". |
+----------------------------------+-------------------------------------------------+
| | In general, *t1* * i == *t1* * (i-1) + *t1* is |
| | true. (1) |
+----------------------------------+-------------------------------------------------+
| "t1 = t2 * f or t1 = f * t2" | Delta multiplied by a float. The result is |
| | rounded to the nearest multiple of |
| | timedelta.resolution using round-half-to-even. |
+----------------------------------+-------------------------------------------------+
| "f = t2 / t3" | Division (3) of *t2* by *t3*. Returns a |
| | "float" object. |
+----------------------------------+-------------------------------------------------+
| "t1 = t2 / f or t1 = t2 / i" | Delta divided by a float or an int. The result |
| | is rounded to the nearest multiple of |
| | timedelta.resolution using round-half-to-even. |
+----------------------------------+-------------------------------------------------+
| "t1 = t2 // i" or "t1 = t2 // | The floor is computed and the remainder (if |
| t3" | any) is thrown away. In the second case, an |
| | integer is returned. (3) |
+----------------------------------+-------------------------------------------------+
| "t1 = t2 % t3" | The remainder is computed as a "timedelta" |
| | object. (3) |
+----------------------------------+-------------------------------------------------+
| "q, r = divmod(t1, t2)" | Computes the quotient and the remainder: "q = |
| | t1 // t2" (3) and "r = t1 % t2". q is an |
| | integer and r is a "timedelta" object. |
+----------------------------------+-------------------------------------------------+
| "+t1" | Returns a "timedelta" object with the same |
| | value. (2) |
+----------------------------------+-------------------------------------------------+
| "-t1" | equivalent to "timedelta"(-*t1.days*, |
| | -*t1.seconds*, -*t1.microseconds*), and to |
| | *t1** -1. (1)(4) |
+----------------------------------+-------------------------------------------------+
| "abs(t)" | equivalent to +*t* when "t.days >= 0", and to |
| | -*t* when "t.days < 0". (2) |
+----------------------------------+-------------------------------------------------+
| "str(t)" | Returns a string in the form "[D day[s], |
| | ][H]H:MM:SS[.UUUUUU]", where D is negative for |
| | negative "t". (5) |
+----------------------------------+-------------------------------------------------+
| "repr(t)" | Returns a string in the form |
| | "datetime.timedelta(D[, S[, U]])", where D is |
| | negative for negative "t". (5) |
+----------------------------------+-------------------------------------------------+

Notes:

1. This is exact, but may overflow.

2. This is exact, and cannot overflow.

3. Division by 0 raises "ZeroDivisionError".

4. -*timedelta.max* is not representable as a "timedelta" object.

5. String representations of "timedelta" objects are normalized
similarly to their internal representation. This leads to somewhat
unusual results for negative timedeltas. For example:

>>> timedelta(hours=-5)
datetime.timedelta(-1, 68400)
>>> print(_)
-1 day, 19:00:00

In addition to the operations listed above "timedelta" objects support
certain additions and subtractions with "date" and "datetime" objects
(see below).

Changed in version 3.2: Floor division and true division of a
"timedelta" object by another "timedelta" object are now supported, as
are remainder operations and the "divmod()" function. True division
and multiplication of a "timedelta" object by a "float" object are now
supported.

Comparisons of "timedelta" objects are supported with the "timedelta"
object representing the smaller duration considered to be the smaller
timedelta. In order to stop mixed-type comparisons from falling back
to the default comparison by object address, when a "timedelta" object
is compared to an object of a different type, "TypeError" is raised
unless the comparison is "==" or "!=". The latter cases return
"False" or "True", respectively.

"timedelta" objects are *hashable* (usable as dictionary keys),
support efficient pickling, and in Boolean contexts, a "timedelta"
object is considered to be true if and only if it isn’t equal to
"timedelta(0)".

Instance methods:

timedelta.total_seconds()

Return the total number of seconds contained in the duration.
Equivalent to "td / timedelta(seconds=1)".

Note that for very large time intervals (greater than 270 years on
most platforms) this method will lose microsecond accuracy.

New in version 3.2.

Example usage:

>>> from datetime import timedelta
>>> year = timedelta(days=365)
>>> another_year = timedelta(weeks=40, days=84, hours=23,
... minutes=50, seconds=600) # adds up to 365 days
>>> year.total_seconds()
31536000.0
>>> year == another_year
True
>>> ten_years = 10 * year
>>> ten_years, ten_years.days // 365
(datetime.timedelta(3650), 10)
>>> nine_years = ten_years - year
>>> nine_years, nine_years.days // 365
(datetime.timedelta(3285), 9)
>>> three_years = nine_years // 3;
>>> three_years, three_years.days // 365
(datetime.timedelta(1095), 3)
>>> abs(three_years - ten_years) == 2 * three_years + year
True

"date" Objects
==============

A "date" object represents a date (year, month and day) in an
idealized calendar, the current Gregorian calendar indefinitely
extended in both directions. January 1 of year 1 is called day number
1, January 2 of year 1 is called day number 2, and so on. This
matches the definition of the “proleptic Gregorian” calendar in
Dershowitz and Reingold’s book Calendrical Calculations, where it’s
the base calendar for all computations. See the book for algorithms
for converting between proleptic Gregorian ordinals and many other
calendar systems.

class datetime.date(year, month, day)

All arguments are required. Arguments may be integers, in the
following ranges:

* "MINYEAR <= year <= MAXYEAR"

* "1 <= month <= 12"

* "1 <= day <= number of days in the given month and year"

If an argument outside those ranges is given, "ValueError" is
raised.

Other constructors, all class methods:

classmethod date.today()

Return the current local date. This is equivalent to
"date.fromtimestamp(time.time())".

classmethod date.fromtimestamp(timestamp)

Return the local date corresponding to the POSIX timestamp, such as
is returned by "time.time()". This may raise "OverflowError", if
the timestamp is out of the range of values supported by the
platform C "localtime()" function, and "OSError" on "localtime()"
failure. It’s common for this to be restricted to years from 1970
through 2038. Note that on non-POSIX systems that include leap
seconds in their notion of a timestamp, leap seconds are ignored by
"fromtimestamp()".

Changed in version 3.3: Raise "OverflowError" instead of
"ValueError" if the timestamp is out of the range of values
supported by the platform C "localtime()" function. Raise "OSError"
instead of "ValueError" on "localtime()" failure.

classmethod date.fromordinal(ordinal)

Return the date corresponding to the proleptic Gregorian ordinal,
where January 1 of year 1 has ordinal 1. "ValueError" is raised
unless "1 <= ordinal <= date.max.toordinal()". For any date *d*,
"date.fromordinal(d.toordinal()) == d".

Class attributes:

date.min

The earliest representable date, "date(MINYEAR, 1, 1)".

date.max

The latest representable date, "date(MAXYEAR, 12, 31)".

date.resolution

The smallest possible difference between non-equal date objects,
"timedelta(days=1)".

Instance attributes (read-only):

date.year

Between "MINYEAR" and "MAXYEAR" inclusive.

date.month

Between 1 and 12 inclusive.

date.day

Between 1 and the number of days in the given month of the given
year.

Supported operations:

+---------------------------------+------------------------------------------------+
| Operation | Result |
+=================================+================================================+
| "date2 = date1 + timedelta" | *date2* is "timedelta.days" days removed from |
| | *date1*. (1) |
+---------------------------------+------------------------------------------------+
| "date2 = date1 - timedelta" | Computes *date2* such that "date2 + timedelta |
| | == date1". (2) |
+---------------------------------+------------------------------------------------+
| "timedelta = date1 - date2" | (3) |
+---------------------------------+------------------------------------------------+
| "date1 < date2" | *date1* is considered less than *date2* when |
| | *date1* precedes *date2* in time. (4) |
+---------------------------------+------------------------------------------------+

Notes:

1. *date2* is moved forward in time if "timedelta.days > 0", or
backward if "timedelta.days < 0". Afterward "date2 - date1 ==
timedelta.days". "timedelta.seconds" and "timedelta.microseconds"
are ignored. "OverflowError" is raised if "date2.year" would be
smaller than "MINYEAR" or larger than "MAXYEAR".

2. This isn’t quite equivalent to date1 + (-timedelta), because
-timedelta in isolation can overflow in cases where date1 -
timedelta does not. "timedelta.seconds" and
"timedelta.microseconds" are ignored.

3. This is exact, and cannot overflow. timedelta.seconds and
timedelta.microseconds are 0, and date2 + timedelta == date1 after.

4. In other words, "date1 < date2" if and only if
"date1.toordinal() < date2.toordinal()". In order to stop
comparison from falling back to the default scheme of comparing
object addresses, date comparison normally raises "TypeError" if
the other comparand isn’t also a "date" object. However,
"NotImplemented" is returned instead if the other comparand has a
"timetuple()" attribute. This hook gives other kinds of date
objects a chance at implementing mixed- type comparison. If not,
when a "date" object is compared to an object of a different type,
"TypeError" is raised unless the comparison is "==" or "!=". The
latter cases return "False" or "True", respectively.

Dates can be used as dictionary keys. In Boolean contexts, all "date"
objects are considered to be true.

Instance methods:

date.replace(year=self.year, month=self.month, day=self.day)

Return a date with the same value, except for those parameters
given new values by whichever keyword arguments are specified. For
example, if "d == date(2002, 12, 31)", then "d.replace(day=26) ==
date(2002, 12, 26)".

date.timetuple()

Return a "time.struct_time" such as returned by "time.localtime()".
The hours, minutes and seconds are 0, and the DST flag is -1.
"d.timetuple()" is equivalent to "time.struct_time((d.year,
d.month, d.day, 0, 0, 0, d.weekday(), yday, -1))", where "yday =
d.toordinal() - date(d.year, 1, 1).toordinal() + 1" is the day
number within the current year starting with "1" for January 1st.

date.toordinal()

Return the proleptic Gregorian ordinal of the date, where January 1
of year 1 has ordinal 1. For any "date" object *d*,
"date.fromordinal(d.toordinal()) == d".

date.weekday()

Return the day of the week as an integer, where Monday is 0 and
Sunday is 6. For example, "date(2002, 12, 4).weekday() == 2", a
Wednesday. See also "isoweekday()".

date.isoweekday()

Return the day of the week as an integer, where Monday is 1 and
Sunday is 7. For example, "date(2002, 12, 4).isoweekday() == 3", a
Wednesday. See also "weekday()", "isocalendar()".

date.isocalendar()

Return a 3-tuple, (ISO year, ISO week number, ISO weekday).

The ISO calendar is a widely used variant of the Gregorian
calendar. See
https://www.staff.science.uu.nl/~gent0113/calendar/isocalendar.htm
for a good explanation.

The ISO year consists of 52 or 53 full weeks, and where a week
starts on a Monday and ends on a Sunday. The first week of an ISO
year is the first (Gregorian) calendar week of a year containing a
Thursday. This is called week number 1, and the ISO year of that
Thursday is the same as its Gregorian year.

For example, 2004 begins on a Thursday, so the first week of ISO
year 2004 begins on Monday, 29 Dec 2003 and ends on Sunday, 4 Jan
2004, so that "date(2003, 12, 29).isocalendar() == (2004, 1, 1)"
and "date(2004, 1, 4).isocalendar() == (2004, 1, 7)".

date.isoformat()

Return a string representing the date in ISO 8601 format, ‘YYYY-MM-
DD’. For example, "date(2002, 12, 4).isoformat() == '2002-12-04'".

date.__str__()

For a date *d*, "str(d)" is equivalent to "d.isoformat()".

date.ctime()

Return a string representing the date, for example "date(2002, 12,
4).ctime() == 'Wed Dec 4 00:00:00 2002'". "d.ctime()" is equivalent
to "time.ctime(time.mktime(d.timetuple()))" on platforms where the
native C "ctime()" function (which "time.ctime()" invokes, but
which "date.ctime()" does not invoke) conforms to the C standard.

date.strftime(format)

Return a string representing the date, controlled by an explicit
format string. Format codes referring to hours, minutes or seconds
will see 0 values. For a complete list of formatting directives,
see strftime() and strptime() Behavior.

date.__format__(format)

Same as "date.strftime()". This makes it possible to specify a
format string for a "date" object in formatted string literals and
when using "str.format()". For a complete list of formatting
directives, see strftime() and strptime() Behavior.

Example of counting days to an event:

>>> import time
>>> from datetime import date
>>> today = date.today()
>>> today
datetime.date(2007, 12, 5)
>>> today == date.fromtimestamp(time.time())
True
>>> my_birthday = date(today.year, 6, 24)
>>> if my_birthday < today:
... my_birthday = my_birthday.replace(year=today.year + 1)
>>> my_birthday
datetime.date(2008, 6, 24)
>>> time_to_birthday = abs(my_birthday - today)
>>> time_to_birthday.days
202

Example of working with "date":

>>> from datetime import date
>>> d = date.fromordinal(730920) # 730920th day after 1. 1. 0001
>>> d
datetime.date(2002, 3, 11)
>>> t = d.timetuple()
>>> for i in t:
... print(i)
2002 # year
3 # month
11 # day
0
0
0
0 # weekday (0 = Monday)
70 # 70th day in the year
-1
>>> ic = d.isocalendar()
>>> for i in ic:
... print(i)
2002 # ISO year
11 # ISO week number
1 # ISO day number ( 1 = Monday )
>>> d.isoformat()
'2002-03-11'
>>> d.strftime("%d/%m/%y")
'11/03/02'
>>> d.strftime("%A %d. %B %Y")
'Monday 11. March 2002'
>>> 'The {1} is {0:%d}, the {2} is {0:%B}.'.format(d, "day", "month")
'The day is 11, the month is March.'

"datetime" Objects
==================

A "datetime" object is a single object containing all the information
from a "date" object and a "time" object. Like a "date" object,
"datetime" assumes the current Gregorian calendar extended in both
directions; like a time object, "datetime" assumes there are exactly
3600*24 seconds in every day.

Constructor:

class datetime.datetime(year, month, day, hour=0, minute=0, second=0, microsecond=0, tzinfo=None, *, fold=0)

The year, month and day arguments are required. *tzinfo* may be
"None", or an instance of a "tzinfo" subclass. The remaining
arguments may be integers, in the following ranges:

* "MINYEAR <= year <= MAXYEAR",

* "1 <= month <= 12",

* "1 <= day <= number of days in the given month and year",

* "0 <= hour < 24",

* "0 <= minute < 60",

* "0 <= second < 60",

* "0 <= microsecond < 1000000",

* "fold in [0, 1]".

If an argument outside those ranges is given, "ValueError" is
raised.

New in version 3.6: Added the "fold" argument.

Other constructors, all class methods:

classmethod datetime.today()

Return the current local datetime, with "tzinfo" "None". This is
equivalent to "datetime.fromtimestamp(time.time())". See also
"now()", "fromtimestamp()".

classmethod datetime.now(tz=None)

Return the current local date and time. If optional argument *tz*
is "None" or not specified, this is like "today()", but, if
possible, supplies more precision than can be gotten from going
through a "time.time()" timestamp (for example, this may be
possible on platforms supplying the C "gettimeofday()" function).

If *tz* is not "None", it must be an instance of a "tzinfo"
subclass, and the current date and time are converted to *tz*’s
time zone. In this case the result is equivalent to
"tz.fromutc(datetime.utcnow().replace(tzinfo=tz))". See also
"today()", "utcnow()".

classmethod datetime.utcnow()

Return the current UTC date and time, with "tzinfo" "None". This is
like "now()", but returns the current UTC date and time, as a naive
"datetime" object. An aware current UTC datetime can be obtained
by calling "datetime.now(timezone.utc)". See also "now()".

classmethod datetime.fromtimestamp(timestamp, tz=None)

Return the local date and time corresponding to the POSIX
timestamp, such as is returned by "time.time()". If optional
argument *tz* is "None" or not specified, the timestamp is
converted to the platform’s local date and time, and the returned
"datetime" object is naive.

If *tz* is not "None", it must be an instance of a "tzinfo"
subclass, and the timestamp is converted to *tz*’s time zone. In
this case the result is equivalent to "tz.fromutc(datetime.utcfrom
timestamp(timestamp).replace(tzinfo=tz))".

"fromtimestamp()" may raise "OverflowError", if the timestamp is
out of the range of values supported by the platform C
"localtime()" or "gmtime()" functions, and "OSError" on
"localtime()" or "gmtime()" failure. It’s common for this to be
restricted to years in 1970 through 2038. Note that on non-POSIX
systems that include leap seconds in their notion of a timestamp,
leap seconds are ignored by "fromtimestamp()", and then it’s
possible to have two timestamps differing by a second that yield
identical "datetime" objects. See also "utcfromtimestamp()".

Changed in version 3.3: Raise "OverflowError" instead of
"ValueError" if the timestamp is out of the range of values
supported by the platform C "localtime()" or "gmtime()" functions.
Raise "OSError" instead of "ValueError" on "localtime()" or
"gmtime()" failure.

Changed in version 3.6: "fromtimestamp()" may return instances with
"fold" set to 1.

classmethod datetime.utcfromtimestamp(timestamp)

Return the UTC "datetime" corresponding to the POSIX timestamp,
with "tzinfo" "None". This may raise "OverflowError", if the
timestamp is out of the range of values supported by the platform C
"gmtime()" function, and "OSError" on "gmtime()" failure. It’s
common for this to be restricted to years in 1970 through 2038.

To get an aware "datetime" object, call "fromtimestamp()":

datetime.fromtimestamp(timestamp, timezone.utc)

On the POSIX compliant platforms, it is equivalent to the following
expression:

datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=timestamp)

except the latter formula always supports the full years range:
between "MINYEAR" and "MAXYEAR" inclusive.

Changed in version 3.3: Raise "OverflowError" instead of
"ValueError" if the timestamp is out of the range of values
supported by the platform C "gmtime()" function. Raise "OSError"
instead of "ValueError" on "gmtime()" failure.

classmethod datetime.fromordinal(ordinal)

Return the "datetime" corresponding to the proleptic Gregorian
ordinal, where January 1 of year 1 has ordinal 1. "ValueError" is
raised unless "1 <= ordinal <= datetime.max.toordinal()". The
hour, minute, second and microsecond of the result are all 0, and
"tzinfo" is "None".

classmethod datetime.combine(date, time, tzinfo=self.tzinfo)

Return a new "datetime" object whose date components are equal to
the given "date" object’s, and whose time components are equal to
the given "time" object’s. If the *tzinfo* argument is provided,
its value is used to set the "tzinfo" attribute of the result,
otherwise the "tzinfo" attribute of the *time* argument is used.

For any "datetime" object *d*, "d == datetime.combine(d.date(),
d.time(), d.tzinfo)". If date is a "datetime" object, its time
components and "tzinfo" attributes are ignored.

Changed in version 3.6: Added the *tzinfo* argument.

classmethod datetime.strptime(date_string, format)

Return a "datetime" corresponding to *date_string*, parsed
according to *format*. This is equivalent to
"datetime(*(time.strptime(date_string, format)[0:6]))".
"ValueError" is raised if the date_string and format can’t be
parsed by "time.strptime()" or if it returns a value which isn’t a
time tuple. For a complete list of formatting directives, see
strftime() and strptime() Behavior.

Class attributes:

datetime.min

The earliest representable "datetime", "datetime(MINYEAR, 1, 1,
tzinfo=None)".

datetime.max

The latest representable "datetime", "datetime(MAXYEAR, 12, 31, 23,
59, 59, 999999, tzinfo=None)".

datetime.resolution

The smallest possible difference between non-equal "datetime"
objects, "timedelta(microseconds=1)".

Instance attributes (read-only):

datetime.year

Between "MINYEAR" and "MAXYEAR" inclusive.

datetime.month

Between 1 and 12 inclusive.

datetime.day

Between 1 and the number of days in the given month of the given
year.

datetime.hour

In "range(24)".

datetime.minute

In "range(60)".

datetime.second

In "range(60)".

datetime.microsecond

In "range(1000000)".

datetime.tzinfo

The object passed as the *tzinfo* argument to the "datetime"
constructor, or "None" if none was passed.

datetime.fold

In "[0, 1]". Used to disambiguate wall times during a repeated
interval. (A repeated interval occurs when clocks are rolled back
at the end of daylight saving time or when the UTC offset for the
current zone is decreased for political reasons.) The value 0 (1)
represents the earlier (later) of the two moments with the same
wall time representation.

New in version 3.6.

Supported operations:

+-----------------------------------------+----------------------------------+
| Operation | Result |
+=========================================+==================================+
| "datetime2 = datetime1 + timedelta" | (1) |
+-----------------------------------------+----------------------------------+
| "datetime2 = datetime1 - timedelta" | (2) |
+-----------------------------------------+----------------------------------+
| "timedelta = datetime1 - datetime2" | (3) |
+-----------------------------------------+----------------------------------+
| "datetime1 < datetime2" | Compares "datetime" to |
| | "datetime". (4) |
+-----------------------------------------+----------------------------------+

1. datetime2 is a duration of timedelta removed from datetime1,
moving forward in time if "timedelta.days" > 0, or backward if
"timedelta.days" < 0. The result has the same "tzinfo" attribute
as the input datetime, and datetime2 - datetime1 == timedelta
after. "OverflowError" is raised if datetime2.year would be smaller
than "MINYEAR" or larger than "MAXYEAR". Note that no time zone
adjustments are done even if the input is an aware object.

2. Computes the datetime2 such that datetime2 + timedelta ==
datetime1. As for addition, the result has the same "tzinfo"
attribute as the input datetime, and no time zone adjustments are
done even if the input is aware. This isn’t quite equivalent to
datetime1 + (-timedelta), because -timedelta in isolation can
overflow in cases where datetime1 - timedelta does not.

3. Subtraction of a "datetime" from a "datetime" is defined only if
both operands are naive, or if both are aware. If one is aware and
the other is naive, "TypeError" is raised.

If both are naive, or both are aware and have the same "tzinfo"
attribute, the "tzinfo" attributes are ignored, and the result is a
"timedelta" object *t* such that "datetime2 + t == datetime1". No
time zone adjustments are done in this case.

If both are aware and have different "tzinfo" attributes, "a-b"
acts as if *a* and *b* were first converted to naive UTC datetimes
first. The result is "(a.replace(tzinfo=None) - a.utcoffset()) -
(b.replace(tzinfo=None) - b.utcoffset())" except that the
implementation never overflows.

4. *datetime1* is considered less than *datetime2* when *datetime1*
precedes *datetime2* in time.

If one comparand is naive and the other is aware, "TypeError" is
raised if an order comparison is attempted. For equality
comparisons, naive instances are never equal to aware instances.

If both comparands are aware, and have the same "tzinfo" attribute,
the common "tzinfo" attribute is ignored and the base datetimes are
compared. If both comparands are aware and have different "tzinfo"
attributes, the comparands are first adjusted by subtracting their
UTC offsets (obtained from "self.utcoffset()").

Changed in version 3.3: Equality comparisons between naive and
aware "datetime" instances don’t raise "TypeError".

Note: In order to stop comparison from falling back to the
default scheme of comparing object addresses, datetime comparison
normally raises "TypeError" if the other comparand isn’t also a
"datetime" object. However, "NotImplemented" is returned instead
if the other comparand has a "timetuple()" attribute. This hook
gives other kinds of date objects a chance at implementing mixed-
type comparison. If not, when a "datetime" object is compared to
an object of a different type, "TypeError" is raised unless the
comparison is "==" or "!=". The latter cases return "False" or
"True", respectively.

"datetime" objects can be used as dictionary keys. In Boolean
contexts, all "datetime" objects are considered to be true.

Instance methods:

datetime.date()

Return "date" object with same year, month and day.

datetime.time()

Return "time" object with same hour, minute, second, microsecond
and fold. "tzinfo" is "None". See also method "timetz()".

Changed in version 3.6: The fold value is copied to the returned
"time" object.

datetime.timetz()

Return "time" object with same hour, minute, second, microsecond,
fold, and tzinfo attributes. See also method "time()".

Changed in version 3.6: The fold value is copied to the returned
"time" object.

datetime.replace(year=self.year, month=self.month, day=self.day, hour=self.hour, minute=self.minute, second=self.second, microsecond=self.microsecond, tzinfo=self.tzinfo, * fold=0)

Return a datetime with the same attributes, except for those
attributes given new values by whichever keyword arguments are
specified. Note that "tzinfo=None" can be specified to create a
naive datetime from an aware datetime with no conversion of date
and time data.

New in version 3.6: Added the "fold" argument.

datetime.astimezone(tz=None)

Return a "datetime" object with new "tzinfo" attribute *tz*,
adjusting the date and time data so the result is the same UTC time
as *self*, but in *tz*’s local time.

If provided, *tz* must be an instance of a "tzinfo" subclass, and
its "utcoffset()" and "dst()" methods must not return "None". If
*self* is naive ("self.tzinfo is None"), it is presumed to
represent time in the system timezone.

If called without arguments (or with "tz=None") the system local
timezone is assumed for the target timezone. The ".tzinfo"
attribute of the converted datetime instance will be set to an
instance of "timezone" with the zone name and offset obtained from
the OS.

If "self.tzinfo" is *tz*, "self.astimezone(tz)" is equal to *self*:
no adjustment of date or time data is performed. Else the result is
local time in the timezone *tz*, representing the same UTC time as
*self*: after "astz = dt.astimezone(tz)", "astz -
astz.utcoffset()" will have the same date and time data as "dt -
dt.utcoffset()".

If you merely want to attach a time zone object *tz* to a datetime
*dt* without adjustment of date and time data, use
"dt.replace(tzinfo=tz)". If you merely want to remove the time
zone object from an aware datetime *dt* without conversion of date
and time data, use "dt.replace(tzinfo=None)".

Note that the default "tzinfo.fromutc()" method can be overridden
in a "tzinfo" subclass to affect the result returned by
"astimezone()". Ignoring error cases, "astimezone()" acts like:

def astimezone(self, tz):
if self.tzinfo is tz:
return self
# Convert self to UTC, and attach the new time zone object.
utc = (self - self.utcoffset()).replace(tzinfo=tz)
# Convert from UTC to tz's local time.
return tz.fromutc(utc)

Changed in version 3.3: *tz* now can be omitted.

Changed in version 3.6: The "astimezone()" method can now be called
on naive instances that are presumed to represent system local
time.

datetime.utcoffset()

If "tzinfo" is "None", returns "None", else returns
"self.tzinfo.utcoffset(self)", and raises an exception if the
latter doesn’t return "None", or a "timedelta" object representing
a whole number of minutes with magnitude less than one day.

datetime.dst()

If "tzinfo" is "None", returns "None", else returns
"self.tzinfo.dst(self)", and raises an exception if the latter
doesn’t return "None", or a "timedelta" object representing a whole
number of minutes with magnitude less than one day.

datetime.tzname()

If "tzinfo" is "None", returns "None", else returns
"self.tzinfo.tzname(self)", raises an exception if the latter
doesn’t return "None" or a string object,

datetime.timetuple()

Return a "time.struct_time" such as returned by "time.localtime()".
"d.timetuple()" is equivalent to "time.struct_time((d.year,
d.month, d.day, d.hour, d.minute, d.second, d.weekday(), yday,
dst))", where "yday = d.toordinal() - date(d.year, 1,
1).toordinal() + 1" is the day number within the current year
starting with "1" for January 1st. The "tm_isdst" flag of the
result is set according to the "dst()" method: "tzinfo" is "None"
or "dst()" returns "None", "tm_isdst" is set to "-1"; else if
"dst()" returns a non-zero value, "tm_isdst" is set to "1"; else
"tm_isdst" is set to "0".

datetime.utctimetuple()

If "datetime" instance *d* is naive, this is the same as
"d.timetuple()" except that "tm_isdst" is forced to 0 regardless of
what "d.dst()" returns. DST is never in effect for a UTC time.

If *d* is aware, *d* is normalized to UTC time, by subtracting
"d.utcoffset()", and a "time.struct_time" for the normalized time
is returned. "tm_isdst" is forced to 0. Note that an
"OverflowError" may be raised if *d*.year was "MINYEAR" or
"MAXYEAR" and UTC adjustment spills over a year boundary.

datetime.toordinal()

Return the proleptic Gregorian ordinal of the date. The same as
"self.date().toordinal()".

datetime.timestamp()

Return POSIX timestamp corresponding to the "datetime" instance.
The return value is a "float" similar to that returned by
"time.time()".

Naive "datetime" instances are assumed to represent local time and
this method relies on the platform C "mktime()" function to perform
the conversion. Since "datetime" supports wider range of values
than "mktime()" on many platforms, this method may raise
"OverflowError" for times far in the past or far in the future.

For aware "datetime" instances, the return value is computed as:

(dt - datetime(1970, 1, 1, tzinfo=timezone.utc)).total_seconds()

New in version 3.3.

Changed in version 3.6: The "timestamp()" method uses the "fold"
attribute to disambiguate the times during a repeated interval.

Note: There is no method to obtain the POSIX timestamp directly
from a naive "datetime" instance representing UTC time. If your
application uses this convention and your system timezone is not
set to UTC, you can obtain the POSIX timestamp by supplying
"tzinfo=timezone.utc":

timestamp = dt.replace(tzinfo=timezone.utc).timestamp()

or by calculating the timestamp directly:

timestamp = (dt - datetime(1970, 1, 1)) / timedelta(seconds=1)

datetime.weekday()

Return the day of the week as an integer, where Monday is 0 and
Sunday is 6. The same as "self.date().weekday()". See also
"isoweekday()".

datetime.isoweekday()

Return the day of the week as an integer, where Monday is 1 and
Sunday is 7. The same as "self.date().isoweekday()". See also
"weekday()", "isocalendar()".

datetime.isocalendar()

Return a 3-tuple, (ISO year, ISO week number, ISO weekday). The
same as "self.date().isocalendar()".

datetime.isoformat(sep='T', timespec='auto')

Return a string representing the date and time in ISO 8601 format,
YYYY-MM-DDTHH:MM:SS.mmmmmm or, if "microsecond" is 0, YYYY-MM-
DDTHH:MM:SS

If "utcoffset()" does not return "None", a 6-character string is
appended, giving the UTC offset in (signed) hours and minutes:
YYYY-MM-DDTHH:MM:SS.mmmmmm+HH:MM or, if "microsecond" is 0 YYYY-MM-
DDTHH:MM:SS+HH:MM

The optional argument *sep* (default "'T'") is a one-character
separator, placed between the date and time portions of the result.
For example,

>>> from datetime import tzinfo, timedelta, datetime
>>> class TZ(tzinfo):
... def utcoffset(self, dt): return timedelta(minutes=-399)
...
>>> datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
'2002-12-25 00:00:00-06:39'

The optional argument *timespec* specifies the number of additional
components of the time to include (the default is "'auto'"). It can
be one of the following:

* "'auto'": Same as "'seconds'" if "microsecond" is 0, same as
"'microseconds'" otherwise.

* "'hours'": Include the "hour" in the two-digit HH format.

* "'minutes'": Include "hour" and "minute" in HH:MM format.

* "'seconds'": Include "hour", "minute", and "second" in HH:MM:SS
format.

* "'milliseconds'": Include full time, but truncate fractional
second part to milliseconds. HH:MM:SS.sss format.

* "'microseconds'": Include full time in HH:MM:SS.mmmmmm format.

Note: Excluded time components are truncated, not rounded.

"ValueError" will be raised on an invalid *timespec* argument.

>>> from datetime import datetime
>>> datetime.now().isoformat(timespec='minutes')
'2002-12-25T00:00'
>>> dt = datetime(2015, 1, 1, 12, 30, 59, 0)
>>> dt.isoformat(timespec='microseconds')
'2015-01-01T12:30:59.000000'

New in version 3.6: Added the *timespec* argument.

datetime.__str__()

For a "datetime" instance *d*, "str(d)" is equivalent to
"d.isoformat(' ')".

datetime.ctime()

Return a string representing the date and time, for example
"datetime(2002, 12, 4, 20, 30, 40).ctime() == 'Wed Dec 4 20:30:40
2002'". "d.ctime()" is equivalent to
"time.ctime(time.mktime(d.timetuple()))" on platforms where the
native C "ctime()" function (which "time.ctime()" invokes, but
which "datetime.ctime()" does not invoke) conforms to the C
standard.

datetime.strftime(format)

Return a string representing the date and time, controlled by an
explicit format string. For a complete list of formatting
directives, see strftime() and strptime() Behavior.

datetime.__format__(format)

Same as "datetime.strftime()". This makes it possible to specify a
format string for a "datetime" object in formatted string literals
and when using "str.format()". For a complete list of formatting
directives, see strftime() and strptime() Behavior.

Examples of working with datetime objects:

>>> from datetime import datetime, date, time
>>> # Using datetime.combine()
>>> d = date(2005, 7, 14)
>>> t = time(12, 30)
>>> datetime.combine(d, t)
datetime.datetime(2005, 7, 14, 12, 30)
>>> # Using datetime.now() or datetime.utcnow()
>>> datetime.now()
datetime.datetime(2007, 12, 6, 16, 29, 43, 79043) # GMT +1
>>> datetime.utcnow()
datetime.datetime(2007, 12, 6, 15, 29, 43, 79060)
>>> # Using datetime.strptime()
>>> dt = datetime.strptime("21/11/06 16:30", "%d/%m/%y %H:%M")
>>> dt
datetime.datetime(2006, 11, 21, 16, 30)
>>> # Using datetime.timetuple() to get tuple of all attributes
>>> tt = dt.timetuple()
>>> for it in tt:
... print(it)
...
2006 # year
11 # month
21 # day
16 # hour
30 # minute
0 # second
1 # weekday (0 = Monday)
325 # number of days since 1st January
-1 # dst - method tzinfo.dst() returned None
>>> # Date in ISO format
>>> ic = dt.isocalendar()
>>> for it in ic:
... print(it)
...
2006 # ISO year
47 # ISO week
2 # ISO weekday
>>> # Formatting datetime
>>> dt.strftime("%A, %d. %B %Y %I:%M%p")
'Tuesday, 21. November 2006 04:30PM'
>>> 'The {1} is {0:%d}, the {2} is {0:%B}, the {3} is {0:%I:%M%p}.'.format(dt, "day", "month", "time")
'The day is 21, the month is November, the time is 04:30PM.'

Using datetime with tzinfo:

>>> from datetime import timedelta, datetime, tzinfo
>>> class GMT1(tzinfo):
... def utcoffset(self, dt):
... return timedelta(hours=1) + self.dst(dt)
... def dst(self, dt):
... # DST starts last Sunday in March
... d = datetime(dt.year, 4, 1) # ends last Sunday in October
... self.dston = d - timedelta(days=d.weekday() + 1)
... d = datetime(dt.year, 11, 1)
... self.dstoff = d - timedelta(days=d.weekday() + 1)
... if self.dston <= dt.replace(tzinfo=None) < self.dstoff:
... return timedelta(hours=1)
... else:
... return timedelta(0)
... def tzname(self,dt):
... return "GMT +1"
...
>>> class GMT2(tzinfo):
... def utcoffset(self, dt):
... return timedelta(hours=2) + self.dst(dt)
... def dst(self, dt):
... d = datetime(dt.year, 4, 1)
... self.dston = d - timedelta(days=d.weekday() + 1)
... d = datetime(dt.year, 11, 1)
... self.dstoff = d - timedelta(days=d.weekday() + 1)
... if self.dston <= dt.replace(tzinfo=None) < self.dstoff:
... return timedelta(hours=1)
... else:
... return timedelta(0)
... def tzname(self,dt):
... return "GMT +2"
...
>>> gmt1 = GMT1()
>>> # Daylight Saving Time
>>> dt1 = datetime(2006, 11, 21, 16, 30, tzinfo=gmt1)
>>> dt1.dst()
datetime.timedelta(0)
>>> dt1.utcoffset()
datetime.timedelta(0, 3600)
>>> dt2 = datetime(2006, 6, 14, 13, 0, tzinfo=gmt1)
>>> dt2.dst()
datetime.timedelta(0, 3600)
>>> dt2.utcoffset()
datetime.timedelta(0, 7200)
>>> # Convert datetime to another time zone
>>> dt3 = dt2.astimezone(GMT2())
>>> dt3 # doctest: +ELLIPSIS
datetime.datetime(2006, 6, 14, 14, 0, tzinfo=<GMT2 object at 0x...>)
>>> dt2 # doctest: +ELLIPSIS
datetime.datetime(2006, 6, 14, 13, 0, tzinfo=<GMT1 object at 0x...>)
>>> dt2.utctimetuple() == dt3.utctimetuple()
True

"time" Objects
==============

A time object represents a (local) time of day, independent of any
particular day, and subject to adjustment via a "tzinfo" object.

class datetime.time(hour=0, minute=0, second=0, microsecond=0, tzinfo=None, *, fold=0)

All arguments are optional. *tzinfo* may be "None", or an instance
of a "tzinfo" subclass. The remaining arguments may be integers,
in the following ranges:

* "0 <= hour < 24",

* "0 <= minute < 60",

* "0 <= second < 60",

* "0 <= microsecond < 1000000",

* "fold in [0, 1]".

If an argument outside those ranges is given, "ValueError" is
raised. All default to "0" except *tzinfo*, which defaults to
"None".

Class attributes:

time.min

The earliest representable "time", "time(0, 0, 0, 0)".

time.max

The latest representable "time", "time(23, 59, 59, 999999)".

time.resolution

The smallest possible difference between non-equal "time" objects,
"timedelta(microseconds=1)", although note that arithmetic on
"time" objects is not supported.

Instance attributes (read-only):

time.hour

In "range(24)".

time.minute

In "range(60)".

time.second

In "range(60)".

time.microsecond

In "range(1000000)".

time.tzinfo

The object passed as the tzinfo argument to the "time" constructor,
or "None" if none was passed.

time.fold

New in version 3.6.

Supported operations:

* comparison of "time" to "time", where *a* is considered less than
*b* when *a* precedes *b* in time. If one comparand is naive and
the other is aware, "TypeError" is raised if an order comparison is
attempted. For equality comparisons, naive instances are never equal
to aware instances.

If both comparands are aware, and have the same "tzinfo" attribute,
the common "tzinfo" attribute is ignored and the base times are
compared. If both comparands are aware and have different "tzinfo"
attributes, the comparands are first adjusted by subtracting their
UTC offsets (obtained from "self.utcoffset()"). In order to stop
mixed-type comparisons from falling back to the default comparison
by object address, when a "time" object is compared to an object of
a different type, "TypeError" is raised unless the comparison is
"==" or "!=". The latter cases return "False" or "True",
respectively.

Changed in version 3.3: Equality comparisons between naive and aware
"time" instances don’t raise "TypeError".

* hash, use as dict key

* efficient pickling

In boolean contexts, a "time" object is always considered to be true.

Changed in version 3.5: Before Python 3.5, a "time" object was
considered to be false if it represented midnight in UTC. This
behavior was considered obscure and error-prone and has been removed
in Python 3.5. See bpo-13936 for full details.

Instance methods:

time.replace(hour=self.hour, minute=self.minute, second=self.second, microsecond=self.microsecond, tzinfo=self.tzinfo, * fold=0)

Return a "time" with the same value, except for those attributes
given new values by whichever keyword arguments are specified.
Note that "tzinfo=None" can be specified to create a naive "time"
from an aware "time", without conversion of the time data.

New in version 3.6: Added the "fold" argument.

time.isoformat(timespec='auto')

Return a string representing the time in ISO 8601 format,
HH:MM:SS.mmmmmm or, if "microsecond" is 0, HH:MM:SS If
"utcoffset()" does not return "None", a 6-character string is
appended, giving the UTC offset in (signed) hours and minutes:
HH:MM:SS.mmmmmm+HH:MM or, if self.microsecond is 0, HH:MM:SS+HH:MM

The optional argument *timespec* specifies the number of additional
components of the time to include (the default is "'auto'"). It can
be one of the following:

* "'auto'": Same as "'seconds'" if "microsecond" is 0, same as
"'microseconds'" otherwise.

* "'hours'": Include the "hour" in the two-digit HH format.

* "'minutes'": Include "hour" and "minute" in HH:MM format.

* "'seconds'": Include "hour", "minute", and "second" in HH:MM:SS
format.

* "'milliseconds'": Include full time, but truncate fractional
second part to milliseconds. HH:MM:SS.sss format.

* "'microseconds'": Include full time in HH:MM:SS.mmmmmm format.

Note: Excluded time components are truncated, not rounded.

"ValueError" will be raised on an invalid *timespec* argument.

>>> from datetime import time
>>> time(hour=12, minute=34, second=56, microsecond=123456).isoformat(timespec='minutes')
'12:34'
>>> dt = time(hour=12, minute=34, second=56, microsecond=0)
>>> dt.isoformat(timespec='microseconds')
'12:34:56.000000'
>>> dt.isoformat(timespec='auto')
'12:34:56'

New in version 3.6: Added the *timespec* argument.

time.__str__()

For a time *t*, "str(t)" is equivalent to "t.isoformat()".

time.strftime(format)

Return a string representing the time, controlled by an explicit
format string. For a complete list of formatting directives, see
strftime() and strptime() Behavior.

time.__format__(format)

Same as "time.strftime()". This makes it possible to specify a
format string for a "time" object in formatted string literals and
when using "str.format()". For a complete list of formatting
directives, see strftime() and strptime() Behavior.

time.utcoffset()

If "tzinfo" is "None", returns "None", else returns
"self.tzinfo.utcoffset(None)", and raises an exception if the
latter doesn’t return "None" or a "timedelta" object representing a
whole number of minutes with magnitude less than one day.

time.dst()

If "tzinfo" is "None", returns "None", else returns
"self.tzinfo.dst(None)", and raises an exception if the latter
doesn’t return "None", or a "timedelta" object representing a whole
number of minutes with magnitude less than one day.

time.tzname()

If "tzinfo" is "None", returns "None", else returns
"self.tzinfo.tzname(None)", or raises an exception if the latter
doesn’t return "None" or a string object.

Example:

>>> from datetime import time, tzinfo, timedelta
>>> class GMT1(tzinfo):
... def utcoffset(self, dt):
... return timedelta(hours=1)
... def dst(self, dt):
... return timedelta(0)
... def tzname(self,dt):
... return "Europe/Prague"
...
>>> t = time(12, 10, 30, tzinfo=GMT1())
>>> t # doctest: +ELLIPSIS
datetime.time(12, 10, 30, tzinfo=<GMT1 object at 0x...>)
>>> gmt = GMT1()
>>> t.isoformat()
'12:10:30+01:00'
>>> t.dst()
datetime.timedelta(0)
>>> t.tzname()
'Europe/Prague'
>>> t.strftime("%H:%M:%S %Z")
'12:10:30 Europe/Prague'
>>> 'The {} is {:%H:%M}.'.format("time", t)
'The time is 12:10.'

"tzinfo" Objects
================

class datetime.tzinfo

This is an abstract base class, meaning that this class should not
be instantiated directly. You need to derive a concrete subclass,
and (at least) supply implementations of the standard "tzinfo"
methods needed by the "datetime" methods you use. The "datetime"
module supplies a simple concrete subclass of "tzinfo", "timezone",
which can represent timezones with fixed offset from UTC such as
UTC itself or North American EST and EDT.

An instance of (a concrete subclass of) "tzinfo" can be passed to
the constructors for "datetime" and "time" objects. The latter
objects view their attributes as being in local time, and the
"tzinfo" object supports methods revealing offset of local time
from UTC, the name of the time zone, and DST offset, all relative
to a date or time object passed to them.

Special requirement for pickling: A "tzinfo" subclass must have an
"__init__()" method that can be called with no arguments, else it
can be pickled but possibly not unpickled again. This is a
technical requirement that may be relaxed in the future.

A concrete subclass of "tzinfo" may need to implement the following
methods. Exactly which methods are needed depends on the uses made
of aware "datetime" objects. If in doubt, simply implement all of
them.

tzinfo.utcoffset(dt)

Return offset of local time from UTC, in minutes east of UTC. If
local time is west of UTC, this should be negative. Note that this
is intended to be the total offset from UTC; for example, if a
"tzinfo" object represents both time zone and DST adjustments,
"utcoffset()" should return their sum. If the UTC offset isn’t
known, return "None". Else the value returned must be a
"timedelta" object specifying a whole number of minutes in the
range -1439 to 1439 inclusive (1440 = 24*60; the magnitude of the
offset must be less than one day). Most implementations of
"utcoffset()" will probably look like one of these two:

return CONSTANT # fixed-offset class
return CONSTANT + self.dst(dt) # daylight-aware class

If "utcoffset()" does not return "None", "dst()" should not return
"None" either.

The default implementation of "utcoffset()" raises
"NotImplementedError".

tzinfo.dst(dt)

Return the daylight saving time (DST) adjustment, in minutes east
of UTC, or "None" if DST information isn’t known. Return
"timedelta(0)" if DST is not in effect. If DST is in effect, return
the offset as a "timedelta" object (see "utcoffset()" for details).
Note that DST offset, if applicable, has already been added to the
UTC offset returned by "utcoffset()", so there’s no need to consult
"dst()" unless you’re interested in obtaining DST info separately.
For example, "datetime.timetuple()" calls its "tzinfo" attribute’s
"dst()" method to determine how the "tm_isdst" flag should be set,
and "tzinfo.fromutc()" calls "dst()" to account for DST changes
when crossing time zones.

An instance *tz* of a "tzinfo" subclass that models both standard
and daylight times must be consistent in this sense:

"tz.utcoffset(dt) - tz.dst(dt)"

must return the same result for every "datetime" *dt* with
"dt.tzinfo == tz" For sane "tzinfo" subclasses, this expression
yields the time zone’s “standard offset”, which should not depend
on the date or the time, but only on geographic location. The
implementation of "datetime.astimezone()" relies on this, but
cannot detect violations; it’s the programmer’s responsibility to
ensure it. If a "tzinfo" subclass cannot guarantee this, it may be
able to override the default implementation of "tzinfo.fromutc()"
to work correctly with "astimezone()" regardless.

Most implementations of "dst()" will probably look like one of
these two:

def dst(self, dt):
# a fixed-offset class: doesn't account for DST
return timedelta(0)

def dst(self, dt):
# Code to set dston and dstoff to the time zone's DST
# transition times based on the input dt.year, and expressed
# in standard local time. Then

if dston <= dt.replace(tzinfo=None) < dstoff:
return timedelta(hours=1)
else:
return timedelta(0)

The default implementation of "dst()" raises "NotImplementedError".

tzinfo.tzname(dt)

Return the time zone name corresponding to the "datetime" object
*dt*, as a string. Nothing about string names is defined by the
"datetime" module, and there’s no requirement that it mean anything
in particular. For example, “GMT”, “UTC”, “-500”, “-5:00”, “EDT”,
“US/Eastern”, “America/New York” are all valid replies. Return
"None" if a string name isn’t known. Note that this is a method
rather than a fixed string primarily because some "tzinfo"
subclasses will wish to return different names depending on the
specific value of *dt* passed, especially if the "tzinfo" class is
accounting for daylight time.

The default implementation of "tzname()" raises
"NotImplementedError".

These methods are called by a "datetime" or "time" object, in response
to their methods of the same names. A "datetime" object passes itself
as the argument, and a "time" object passes "None" as the argument. A
"tzinfo" subclass’s methods should therefore be prepared to accept a
*dt* argument of "None", or of class "datetime".

When "None" is passed, it’s up to the class designer to decide the
best response. For example, returning "None" is appropriate if the
class wishes to say that time objects don’t participate in the
"tzinfo" protocols. It may be more useful for "utcoffset(None)" to
return the standard UTC offset, as there is no other convention for
discovering the standard offset.

When a "datetime" object is passed in response to a "datetime" method,
"dt.tzinfo" is the same object as *self*. "tzinfo" methods can rely
on this, unless user code calls "tzinfo" methods directly. The intent
is that the "tzinfo" methods interpret *dt* as being in local time,
and not need worry about objects in other timezones.

There is one more "tzinfo" method that a subclass may wish to
override:

tzinfo.fromutc(dt)

This is called from the default "datetime.astimezone()"
implementation. When called from that, "dt.tzinfo" is *self*, and
*dt*’s date and time data are to be viewed as expressing a UTC
time. The purpose of "fromutc()" is to adjust the date and time
data, returning an equivalent datetime in *self*’s local time.

Most "tzinfo" subclasses should be able to inherit the default
"fromutc()" implementation without problems. It’s strong enough to
handle fixed-offset time zones, and time zones accounting for both
standard and daylight time, and the latter even if the DST
transition times differ in different years. An example of a time
zone the default "fromutc()" implementation may not handle
correctly in all cases is one where the standard offset (from UTC)
depends on the specific date and time passed, which can happen for
political reasons. The default implementations of "astimezone()"
and "fromutc()" may not produce the result you want if the result
is one of the hours straddling the moment the standard offset
changes.

Skipping code for error cases, the default "fromutc()"
implementation acts like:

def fromutc(self, dt):
# raise ValueError error if dt.tzinfo is not self
dtoff = dt.utcoffset()
dtdst = dt.dst()
# raise ValueError if dtoff is None or dtdst is None
delta = dtoff - dtdst # this is self's standard offset
if delta:
dt += delta # convert to standard local time
dtdst = dt.dst()
# raise ValueError if dtdst is None
if dtdst:
return dt + dtdst
else:
return dt

Example "tzinfo" classes:

from datetime import tzinfo, timedelta, datetime, timezone

ZERO = timedelta(0)
HOUR = timedelta(hours=1)
SECOND = timedelta(seconds=1)

# A class capturing the platform's idea of local time.
# (May result in wrong values on historical times in
# timezones where UTC offset and/or the DST rules had
# changed in the past.)
import time as _time

STDOFFSET = timedelta(seconds = -_time.timezone)
if _time.daylight:
DSTOFFSET = timedelta(seconds = -_time.altzone)
else:
DSTOFFSET = STDOFFSET

DSTDIFF = DSTOFFSET - STDOFFSET

class LocalTimezone(tzinfo):

def fromutc(self, dt):
assert dt.tzinfo is self
stamp = (dt - datetime(1970, 1, 1, tzinfo=self)) // SECOND
args = _time.localtime(stamp)[:6]
dst_diff = DSTDIFF // SECOND
# Detect fold
fold = (args == _time.localtime(stamp - dst_diff))
return datetime(*args, microsecond=dt.microsecond,
tzinfo=self, fold=fold)

def utcoffset(self, dt):
if self._isdst(dt):
return DSTOFFSET
else:
return STDOFFSET

def dst(self, dt):
if self._isdst(dt):
return DSTDIFF
else:
return ZERO

def tzname(self, dt):
return _time.tzname[self._isdst(dt)]

def _isdst(self, dt):
tt = (dt.year, dt.month, dt.day,
dt.hour, dt.minute, dt.second,
dt.weekday(), 0, 0)
stamp = _time.mktime(tt)
tt = _time.localtime(stamp)
return tt.tm_isdst > 0

Local = LocalTimezone()

# A complete implementation of current DST rules for major US time zones.

def first_sunday_on_or_after(dt):
days_to_go = 6 - dt.weekday()
if days_to_go:
dt += timedelta(days_to_go)
return dt

# US DST Rules
#
# This is a simplified (i.e., wrong for a few cases) set of rules for US
# DST start and end times. For a complete and up-to-date set of DST rules
# and timezone definitions, visit the Olson Database (or try pytz):
# http://www.twinsun.com/tz/tz-link.htm
# http://sourceforge.net/projects/pytz/ (might not be up-to-date)
#
# In the US, since 2007, DST starts at 2am (standard time) on the second
# Sunday in March, which is the first Sunday on or after Mar 8.
DSTSTART_2007 = datetime(1, 3, 8, 2)
# and ends at 2am (DST time) on the first Sunday of Nov.
DSTEND_2007 = datetime(1, 11, 1, 2)
# From 1987 to 2006, DST used to start at 2am (standard time) on the first
# Sunday in April and to end at 2am (DST time) on the last
# Sunday of October, which is the first Sunday on or after Oct 25.
DSTSTART_1987_2006 = datetime(1, 4, 1, 2)
DSTEND_1987_2006 = datetime(1, 10, 25, 2)
# From 1967 to 1986, DST used to start at 2am (standard time) on the last
# Sunday in April (the one on or after April 24) and to end at 2am (DST time)
# on the last Sunday of October, which is the first Sunday
# on or after Oct 25.
DSTSTART_1967_1986 = datetime(1, 4, 24, 2)
DSTEND_1967_1986 = DSTEND_1987_2006

def us_dst_range(year):
# Find start and end times for US DST. For years before 1967, return
# start = end for no DST.
if 2006 < year:
dststart, dstend = DSTSTART_2007, DSTEND_2007
elif 1986 < year < 2007:
dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006
elif 1966 < year < 1987:
dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986
else:
return (datetime(year, 1, 1), ) * 2

start = first_sunday_on_or_after(dststart.replace(year=year))
end = first_sunday_on_or_after(dstend.replace(year=year))
return start, end

class USTimeZone(tzinfo):

def __init__(self, hours, reprname, stdname, dstname):
self.stdoffset = timedelta(hours=hours)
self.reprname = reprname
self.stdname = stdname
self.dstname = dstname

def __repr__(self):
return self.reprname

def tzname(self, dt):
if self.dst(dt):
return self.dstname
else:
return self.stdname

def utcoffset(self, dt):
return self.stdoffset + self.dst(dt)

def dst(self, dt):
if dt is None or dt.tzinfo is None:
# An exception may be sensible here, in one or both cases.
# It depends on how you want to treat them. The default
# fromutc() implementation (called by the default astimezone()
# implementation) passes a datetime with dt.tzinfo is self.
return ZERO
assert dt.tzinfo is self
start, end = us_dst_range(dt.year)
# Can't compare naive to aware objects, so strip the timezone from
# dt first.
dt = dt.replace(tzinfo=None)
if start + HOUR <= dt < end - HOUR:
# DST is in effect.
return HOUR
if end - HOUR <= dt < end:
# Fold (an ambiguous hour): use dt.fold to disambiguate.
return ZERO if dt.fold else HOUR
if start <= dt < start + HOUR:
# Gap (a non-existent hour): reverse the fold rule.
return HOUR if dt.fold else ZERO
# DST is off.
return ZERO

def fromutc(self, dt):
assert dt.tzinfo is self
start, end = us_dst_range(dt.year)
start = start.replace(tzinfo=self)
end = end.replace(tzinfo=self)
std_time = dt + self.stdoffset
dst_time = std_time + HOUR
if end <= dst_time < end + HOUR:
# Repeated hour
return std_time.replace(fold=1)
if std_time < start or dst_time >= end:
# Standard time
return std_time
if start <= std_time < end - HOUR:
# Daylight saving time
return dst_time

Eastern = USTimeZone(-5, "Eastern", "EST", "EDT")
Central = USTimeZone(-6, "Central", "CST", "CDT")
Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
Pacific = USTimeZone(-8, "Pacific", "PST", "PDT")

Note that there are unavoidable subtleties twice per year in a
"tzinfo" subclass accounting for both standard and daylight time, at
the DST transition points. For concreteness, consider US Eastern (UTC
-0500), where EDT begins the minute after 1:59 (EST) on the second
Sunday in March, and ends the minute after 1:59 (EDT) on the first
Sunday in November:

UTC 3:MM 4:MM 5:MM 6:MM 7:MM 8:MM
EST 22:MM 23:MM 0:MM 1:MM 2:MM 3:MM
EDT 23:MM 0:MM 1:MM 2:MM 3:MM 4:MM

start 22:MM 23:MM 0:MM 1:MM 3:MM 4:MM

end 23:MM 0:MM 1:MM 1:MM 2:MM 3:MM

When DST starts (the “start” line), the local wall clock leaps from
1:59 to 3:00. A wall time of the form 2:MM doesn’t really make sense
on that day, so "astimezone(Eastern)" won’t deliver a result with
"hour == 2" on the day DST begins. For example, at the Spring forward
transition of 2016, we get

>>> u0 = datetime(2016, 3, 13, 5, tzinfo=timezone.utc)
>>> for i in range(4):
... u = u0 + i*HOUR
... t = u.astimezone(Eastern)
... print(u.time(), 'UTC =', t.time(), t.tzname())
...
05:00:00 UTC = 00:00:00 EST
06:00:00 UTC = 01:00:00 EST
07:00:00 UTC = 03:00:00 EDT
08:00:00 UTC = 04:00:00 EDT

When DST ends (the “end” line), there’s a potentially worse problem:
there’s an hour that can’t be spelled unambiguously in local wall
time: the last hour of daylight time. In Eastern, that’s times of the
form 5:MM UTC on the day daylight time ends. The local wall clock
leaps from 1:59 (daylight time) back to 1:00 (standard time) again.
Local times of the form 1:MM are ambiguous. "astimezone()" mimics the
local clock’s behavior by mapping two adjacent UTC hours into the same
local hour then. In the Eastern example, UTC times of the form 5:MM
and 6:MM both map to 1:MM when converted to Eastern, but earlier times
have the "fold" attribute set to 0 and the later times have it set to
1. For example, at the Fall back transition of 2016, we get

>>> u0 = datetime(2016, 11, 6, 4, tzinfo=timezone.utc)
>>> for i in range(4):
... u = u0 + i*HOUR
... t = u.astimezone(Eastern)
... print(u.time(), 'UTC =', t.time(), t.tzname(), t.fold)
...
04:00:00 UTC = 00:00:00 EDT 0
05:00:00 UTC = 01:00:00 EDT 0
06:00:00 UTC = 01:00:00 EST 1
07:00:00 UTC = 02:00:00 EST 0

Note that the "datetime" instances that differ only by the value of
the "fold" attribute are considered equal in comparisons.

Applications that can’t bear wall-time ambiguities should explicitly
check the value of the "fold" attribute or avoid using hybrid "tzinfo"
subclasses; there are no ambiguities when using "timezone", or any
other fixed-offset "tzinfo" subclass (such as a class representing
only EST (fixed offset -5 hours), or only EDT (fixed offset -4
hours)).