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python/vendor/Python-2.7.6/Doc/library/repr.rst
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:mod:`repr` --- Alternate :func:`repr` implementation
.. module:: repr :synopsis: Alternate repr() implementation with size limits.
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
Note
The :mod:`repr` module has been renamed to :mod:`reprlib` in Python 3. The :term:`2to3` tool will automatically adapt imports when converting your sources to Python 3.
Source code: :source:`Lib/repr.py`
The :mod:`repr` 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 which provides formatting services useful in implementing functions similar to the built-in :func:`repr`; size limits for different object types are added to avoid the generation of representations which are excessively long.
.. data:: aRepr This is an instance of :class:`Repr` which is used to provide the :func:`.repr` function described below. Changing the attributes of this object will affect the size limits used by :func:`.repr` and the Python debugger.
.. function:: repr(obj) This is the :meth:`~Repr.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.
Repr Objects
:class:`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.
.. attribute:: Repr.maxlevel Depth limit on the creation of recursive representations. The default is ``6``.
.. attribute:: 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 :attr:`maxdict`, ``5`` for :attr:`maxarray`, and ``6`` for
the others.
.. versionadded:: 2.4
:attr:`maxset`, :attr:`maxfrozenset`, and :attr:`set`.
.. attribute:: Repr.maxlong Maximum number of characters in the representation for a long integer. Digits are dropped from the middle. The default is ``40``.
.. attribute:: 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``.
.. attribute:: Repr.maxother This limit is used to control the size of object types for which no specific formatting method is available on the :class:`Repr` object. It is applied in a similar manner as :attr:`maxstring`. The default is ``20``.
.. method:: Repr.repr(obj) The equivalent to the built-in :func:`repr` that uses the formatting imposed by the instance.
.. method:: Repr.repr1(obj, level) Recursive implementation used by :meth:`.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 :meth:`repr1` to perform recursive formatting, with ``level - 1`` for the value of *level* in the recursive call.
.. method:: Repr.repr_TYPE(obj, level) :noindex: 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 ``string.join(string.split(type(obj).__name__, '_'))``. Dispatch to these methods is handled by :meth:`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 :meth:`Repr.repr1` allows subclasses of :class:`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 repr as reprlib
import sys
class MyRepr(reprlib.Repr):
def repr_file(self, obj, level):
if obj.name in ['<stdin>', '<stdout>', '<stderr>']:
return obj.name
else:
return repr(obj)
aRepr = MyRepr()
print aRepr.repr(sys.stdin) # prints '<stdin>'
