8.19. "repr" — Alternate "repr()" implementation
************************************************

Note:

  The "repr" module has been renamed to "reprlib" in Python 3.  The
  *2to3* tool will automatically adapt imports when converting your
  sources to Python 3.

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

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

The "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 repr.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.

repr.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.

repr.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.


8.19.1. Repr Objects
====================

"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.

   New in version 2.4: "maxset", "maxfrozenset", and "set".

Repr.maxlong

   Maximum number of characters in the representation for a long
   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 "string.join(string.split(type(obj).__name__,
   '_'))". 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)".


8.19.2. 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 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>'
