reprlib — Alternate repr() implementation — Python 3.11.15 documentation
Description: Source code: Lib/reprlib.py 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...

# `reprlib` — Alternate `repr()` implementation

Source code: Lib/reprlib.py

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:

      >>> from reprlib import recursive_repr
      >>> 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

`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.fillvalue

  This string is displayed for recursive references. It defaults to `...`.

  New in version 3.11.

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>'

    <stdin>