8.19. repr — Alternate repr() implementation
The repr module has been renamed to reprlib in Python 3.0. The
2to3 tool will automatically adapt imports when converting your
sources to 3.0.
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 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.
- 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.
- 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 members which can be used to provide
size limits for the representations of different object types, and methods
which format specific object types.
- Depth limit on the creation of recursive representations. The default is 6.
Limits on the number of entries represented for the named object type. The
default is 4 for maxdict, 5 for maxarray, and 6 for
New in version 2.4: maxset, maxfrozenset, and set.
- Maximum number of characters in the representation for a long integer. Digits
are dropped from the middle. The default is 40.
- 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.
- 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.
- The equivalent to the built-in repr() that uses the formatting imposed by
- 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.
- 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
def repr_file(self, obj, level):
if obj.name in ['<stdin>', '<stdout>', '<stderr>']:
aRepr = MyRepr()
print aRepr.repr(sys.stdin) # prints '<stdin>'