160 lines
5.1 KiB
ReStructuredText
160 lines
5.1 KiB
ReStructuredText
:mod:`reprlib` --- Alternate :func:`repr` implementation
|
|
========================================================
|
|
|
|
.. module:: reprlib
|
|
:synopsis: Alternate repr() implementation with size limits.
|
|
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
|
|
|
|
**Source code:** :source:`Lib/reprlib.py`
|
|
|
|
--------------
|
|
|
|
The :mod:`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:: Repr()
|
|
|
|
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.
|
|
|
|
In addition to size-limiting tools, the module also provides a decorator for
|
|
detecting recursive calls to :meth:`__repr__` and substituting a placeholder
|
|
string instead.
|
|
|
|
.. decorator:: recursive_repr(fillvalue="...")
|
|
|
|
Decorator for :meth:`__repr__` methods to detect recursive calls within the
|
|
same thread. If a recursive call is made, the *fillvalue* is returned,
|
|
otherwise, the usual :meth:`__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'>
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. _repr-objects:
|
|
|
|
Repr Objects
|
|
------------
|
|
|
|
:class:`Repr` instances provide several members 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.
|
|
|
|
|
|
.. attribute:: Repr.maxlong
|
|
|
|
Maximum number of characters in the representation for an 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-reprs:
|
|
|
|
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 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>'
|
|
|