Python 3.6.5 Documentation >  "formatter" — Generic output formatting

"formatter" — Generic output formatting
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Deprecated since version 3.4: Due to lack of usage, the formatter
module has been deprecated.

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This module supports two interface definitions, each with multiple
implementations: The *formatter* interface, and the *writer* interface
which is required by the formatter interface.

Formatter objects transform an abstract flow of formatting events into
specific output events on writer objects. Formatters manage several
stack structures to allow various properties of a writer object to be
changed and restored; writers need not be able to handle relative
changes nor any sort of “change back” operation. Specific writer
properties which may be controlled via formatter objects are
horizontal alignment, font, and left margin indentations. A mechanism
is provided which supports providing arbitrary, non-exclusive style
settings to a writer as well. Additional interfaces facilitate
formatting events which are not reversible, such as paragraph
separation.

Writer objects encapsulate device interfaces. Abstract devices, such
as file formats, are supported as well as physical devices. The
provided implementations all work with abstract devices. The
interface makes available mechanisms for setting the properties which
formatter objects manage and inserting data into the output.

The Formatter Interface
=======================

Interfaces to create formatters are dependent on the specific
formatter class being instantiated. The interfaces described below
are the required interfaces which all formatters must support once
initialized.

One data element is defined at the module level:

formatter.AS_IS

Value which can be used in the font specification passed to the
"push_font()" method described below, or as the new value to any
other "push_property()" method. Pushing the "AS_IS" value allows
the corresponding "pop_property()" method to be called without
having to track whether the property was changed.

The following attributes are defined for formatter instance objects:

formatter.writer

The writer instance with which the formatter interacts.

formatter.end_paragraph(blanklines)

Close any open paragraphs and insert at least *blanklines* before
the next paragraph.

formatter.add_line_break()

Add a hard line break if one does not already exist. This does not
break the logical paragraph.

formatter.add_hor_rule(*args, **kw)

Insert a horizontal rule in the output. A hard break is inserted
if there is data in the current paragraph, but the logical
paragraph is not broken. The arguments and keywords are passed on
to the writer’s "send_line_break()" method.

formatter.add_flowing_data(data)

Provide data which should be formatted with collapsed whitespace.
Whitespace from preceding and successive calls to
"add_flowing_data()" is considered as well when the whitespace
collapse is performed. The data which is passed to this method is
expected to be word-wrapped by the output device. Note that any
word-wrapping still must be performed by the writer object due to
the need to rely on device and font information.

formatter.add_literal_data(data)

Provide data which should be passed to the writer unchanged.
Whitespace, including newline and tab characters, are considered
legal in the value of *data*.

formatter.add_label_data(format, counter)

Insert a label which should be placed to the left of the current
left margin. This should be used for constructing bulleted or
numbered lists. If the *format* value is a string, it is
interpreted as a format specification for *counter*, which should
be an integer. The result of this formatting becomes the value of
the label; if *format* is not a string it is used as the label
value directly. The label value is passed as the only argument to
the writer’s "send_label_data()" method. Interpretation of non-
string label values is dependent on the associated writer.

Format specifications are strings which, in combination with a
counter value, are used to compute label values. Each character in
the format string is copied to the label value, with some
characters recognized to indicate a transform on the counter value.
Specifically, the character "'1'" represents the counter value
formatter as an Arabic number, the characters "'A'" and "'a'"
represent alphabetic representations of the counter value in upper
and lower case, respectively, and "'I'" and "'i'" represent the
counter value in Roman numerals, in upper and lower case. Note
that the alphabetic and roman transforms require that the counter
value be greater than zero.

formatter.flush_softspace()

Send any pending whitespace buffered from a previous call to
"add_flowing_data()" to the associated writer object. This should
be called before any direct manipulation of the writer object.

formatter.push_alignment(align)

Push a new alignment setting onto the alignment stack. This may be
"AS_IS" if no change is desired. If the alignment value is changed
from the previous setting, the writer’s "new_alignment()" method is
called with the *align* value.

formatter.pop_alignment()

Restore the previous alignment.

formatter.push_font((size, italic, bold, teletype))

Change some or all font properties of the writer object.
Properties which are not set to "AS_IS" are set to the values
passed in while others are maintained at their current settings.
The writer’s "new_font()" method is called with the fully resolved
font specification.

formatter.pop_font()

Restore the previous font.

formatter.push_margin(margin)

Increase the number of left margin indentations by one, associating
the logical tag *margin* with the new indentation. The initial
margin level is "0". Changed values of the logical tag must be true
values; false values other than "AS_IS" are not sufficient to
change the margin.

formatter.pop_margin()

Restore the previous margin.

formatter.push_style(*styles)

Push any number of arbitrary style specifications. All styles are
pushed onto the styles stack in order. A tuple representing the
entire stack, including "AS_IS" values, is passed to the writer’s
"new_styles()" method.

formatter.pop_style(n=1)

Pop the last *n* style specifications passed to "push_style()". A
tuple representing the revised stack, including "AS_IS" values, is
passed to the writer’s "new_styles()" method.

formatter.set_spacing(spacing)

Set the spacing style for the writer.

formatter.assert_line_data(flag=1)

Inform the formatter that data has been added to the current
paragraph out-of-band. This should be used when the writer has
been manipulated directly. The optional *flag* argument can be set
to false if the writer manipulations produced a hard line break at
the end of the output.

Formatter Implementations
=========================

Two implementations of formatter objects are provided by this module.
Most applications may use one of these classes without modification or
subclassing.

class formatter.NullFormatter(writer=None)

A formatter which does nothing. If *writer* is omitted, a
"NullWriter" instance is created. No methods of the writer are
called by "NullFormatter" instances. Implementations should
inherit from this class if implementing a writer interface but
don’t need to inherit any implementation.

class formatter.AbstractFormatter(writer)

The standard formatter. This implementation has demonstrated wide
applicability to many writers, and may be used directly in most
circumstances. It has been used to implement a full-featured World
Wide Web browser.

The Writer Interface
====================

Interfaces to create writers are dependent on the specific writer
class being instantiated. The interfaces described below are the
required interfaces which all writers must support once initialized.
Note that while most applications can use the "AbstractFormatter"
class as a formatter, the writer must typically be provided by the
application.

writer.flush()

Flush any buffered output or device control events.

writer.new_alignment(align)

Set the alignment style. The *align* value can be any object, but
by convention is a string or "None", where "None" indicates that
the writer’s “preferred” alignment should be used. Conventional
*align* values are "'left'", "'center'", "'right'", and
"'justify'".

writer.new_font(font)

Set the font style. The value of *font* will be "None", indicating
that the device’s default font should be used, or a tuple of the
form "(size, italic, bold, teletype)". Size will be a string
indicating the size of font that should be used; specific strings
and their interpretation must be defined by the application. The
*italic*, *bold*, and *teletype* values are Boolean values
specifying which of those font attributes should be used.

writer.new_margin(margin, level)

Set the margin level to the integer *level* and the logical tag to
*margin*. Interpretation of the logical tag is at the writer’s
discretion; the only restriction on the value of the logical tag is
that it not be a false value for non-zero values of *level*.

writer.new_spacing(spacing)

Set the spacing style to *spacing*.

writer.new_styles(styles)

Set additional styles. The *styles* value is a tuple of arbitrary
values; the value "AS_IS" should be ignored. The *styles* tuple
may be interpreted either as a set or as a stack depending on the
requirements of the application and writer implementation.

writer.send_line_break()

Break the current line.

writer.send_paragraph(blankline)

Produce a paragraph separation of at least *blankline* blank lines,
or the equivalent. The *blankline* value will be an integer. Note
that the implementation will receive a call to "send_line_break()"
before this call if a line break is needed; this method should not
include ending the last line of the paragraph. It is only
responsible for vertical spacing between paragraphs.

writer.send_hor_rule(*args, **kw)

Display a horizontal rule on the output device. The arguments to
this method are entirely application- and writer-specific, and
should be interpreted with care. The method implementation may
assume that a line break has already been issued via
"send_line_break()".

writer.send_flowing_data(data)

Output character data which may be word-wrapped and re-flowed as
needed. Within any sequence of calls to this method, the writer
may assume that spans of multiple whitespace characters have been
collapsed to single space characters.

writer.send_literal_data(data)

Output character data which has already been formatted for display.
Generally, this should be interpreted to mean that line breaks
indicated by newline characters should be preserved and no new line
breaks should be introduced. The data may contain embedded newline
and tab characters, unlike data provided to the
"send_formatted_data()" interface.

writer.send_label_data(data)

Set *data* to the left of the current left margin, if possible. The
value of *data* is not restricted; treatment of non-string values
is entirely application- and writer-dependent. This method will
only be called at the beginning of a line.

Writer Implementations
======================

Three implementations of the writer object interface are provided as
examples by this module. Most applications will need to derive new
writer classes from the "NullWriter" class.

class formatter.NullWriter

A writer which only provides the interface definition; no actions
are taken on any methods. This should be the base class for all
writers which do not need to inherit any implementation methods.

class formatter.AbstractWriter

A writer which can be used in debugging formatters, but not much
else. Each method simply announces itself by printing its name and
arguments on standard output.

class formatter.DumbWriter(file=None, maxcol=72)

Simple writer class which writes output on the *file object* passed
in as *file* or, if *file* is omitted, on standard output. The
output is simply word-wrapped to the number of columns specified by
*maxcol*. This class is suitable for reflowing a sequence of
paragraphs.