Python 3.6.5 Documentation >  "reprlib" — Alternate "repr()" implementation

"reprlib" — Alternate "repr()" implementation
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**Source code:** Lib/reprlib.py

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The "reprlib" module provides a means for producing object
representations with limits on the size of the resulting strings. This
is used in the Python debugger and may be useful in other contexts as
well.

This module provides a class, an instance, and a function:

class reprlib.Repr

Class which provides formatting services useful in implementing
functions similar to the built-in "repr()"; size limits for
different object types are added to avoid the generation of
representations which are excessively long.

reprlib.aRepr

This is an instance of "Repr" which is used to provide the "repr()"
function described below. Changing the attributes of this object
will affect the size limits used by "repr()" and the Python
debugger.

reprlib.repr(obj)

This is the "repr()" method of "aRepr". It returns a string
similar to that returned by the built-in function of the same name,
but with limits on most sizes.

In addition to size-limiting tools, the module also provides a
decorator for detecting recursive calls to "__repr__()" and
substituting a placeholder string instead.

@reprlib.recursive_repr(fillvalue="...")

Decorator for "__repr__()" methods to detect recursive calls within
the same thread. If a recursive call is made, the *fillvalue* is
returned, otherwise, the usual "__repr__()" call is made. For
example:

>>> class MyList(list):
... @recursive_repr()
... def __repr__(self):
... return '<' + '|'.join(map(repr, self)) + '>'
...
>>> m = MyList('abc')
>>> m.append(m)
>>> m.append('x')
>>> print(m)
<'a'|'b'|'c'|...|'x'>

New in version 3.2.

Repr Objects
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"Repr" instances provide several attributes which can be used to
provide size limits for the representations of different object types,
and methods which format specific object types.

Repr.maxlevel

Depth limit on the creation of recursive representations. The
default is "6".

Repr.maxdict
Repr.maxlist
Repr.maxtuple
Repr.maxset
Repr.maxfrozenset
Repr.maxdeque
Repr.maxarray

Limits on the number of entries represented for the named object
type. The default is "4" for "maxdict", "5" for "maxarray", and
"6" for the others.

Repr.maxlong

Maximum number of characters in the representation for an integer.
Digits are dropped from the middle. The default is "40".

Repr.maxstring

Limit on the number of characters in the representation of the
string. Note that the “normal” representation of the string is
used as the character source: if escape sequences are needed in the
representation, these may be mangled when the representation is
shortened. The default is "30".

Repr.maxother

This limit is used to control the size of object types for which no
specific formatting method is available on the "Repr" object. It is
applied in a similar manner as "maxstring". The default is "20".

Repr.repr(obj)

The equivalent to the built-in "repr()" that uses the formatting
imposed by the instance.

Repr.repr1(obj, level)

Recursive implementation used by "repr()". This uses the type of
*obj* to determine which formatting method to call, passing it
*obj* and *level*. The type-specific methods should call "repr1()"
to perform recursive formatting, with "level - 1" for the value of
*level* in the recursive call.

Repr.repr_TYPE(obj, level)

Formatting methods for specific types are implemented as methods
with a name based on the type name. In the method name, **TYPE**
is replaced by "'_'.join(type(obj).__name__.split())". Dispatch to
these methods is handled by "repr1()". Type-specific methods which
need to recursively format a value should call "self.repr1(subobj,
level - 1)".

Subclassing Repr Objects
========================

The use of dynamic dispatching by "Repr.repr1()" allows subclasses of
"Repr" to add support for additional built-in object types or to
modify the handling of types already supported. This example shows how
special support for file objects could be added:

import reprlib
import sys

class MyRepr(reprlib.Repr):

def repr_TextIOWrapper(self, obj, level):
if obj.name in {'<stdin>', '<stdout>', '<stderr>'}:
return obj.name
return repr(obj)

aRepr = MyRepr()
print(aRepr.repr(sys.stdin)) # prints '<stdin>'