Python 3.2+reprlibfunction

reprlib.recursive_repr()

recursive structures

A decorator for __repr__ that guards against infinite recursion: on re-entry for the same object it returns '...'.

Syntax

@reprlib.recursive_repr(fillvalue='...')

Built-in list and dict print [...] for a self-reference on their own, but a custom __repr__ that follows attributes ends in RecursionError on a cycle a.other = b, b.other = a. The decorator tracks (object, thread) pairs, so it also works with threads. Mind the parentheses: @recursive_repr(), while bare @recursive_repr breaks the class.

Examples

import reprlib
class Node:
    @reprlib.recursive_repr()
    def __repr__(self):
        return f'Node({self.other!r})'
a, b = Node(), Node()
a.other, b.other = b, a
print(repr(a))  # → Node(Node(...))

class Node:
    def __repr__(self):
        return f'Node({self.other!r})'
a, b = Node(), Node()
a.other, b.other = b, a
repr(a)  # → RecursionError: maximum recursion depth exceeded

See also

Common errors

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