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reprlib Module

The reprlib module provides an alternative repr() implementation that produces more readable representations of objects, especially useful for long lists or nested structures.

Complexity Reference

Operation Time Space Notes
repr() on list/tuple/deque/array/str O(min(n, k)) O(k) n = input size, k = the relevant max*/maxstring limit.
repr() on dict/set/frozenset O(n) best, O(n log n) worst O(n + k)
recursive_repr() O(1) O(1)

Creating Readable Representations

Truncating Long Outputs

import reprlib

# Create repr with limits - O(1)
repr_obj = reprlib.Repr()
repr_obj.maxlist = 3  # Max list items
repr_obj.maxstring = 20  # Max string length

# Generate representation - O(min(n, k)); a fixed maxlist=3 means this
# would cost the same for a list of 100 or 100 million items
long_list = list(range(100))
result = repr_obj.repr(long_list)
print(result)
# [0, 1, 2, ...]

long_string = "x" * 1000
result = repr_obj.repr(long_string)
print(result)
# 'xxxxxxx...xxxxxxxx'

Default Shorthand

import reprlib

# Using default repr - the whole dict is sorted before the output is
# truncated, so maxdict does not bound the work. O(n) for this dict, whose
# keys are already ascending; scattered keys would make it O(n log n)
large_dict = {i: i**2 for i in range(1000)}
print(reprlib.repr(large_dict))
# {0: 0, 1: 1, 2: 4, 3: 9, ...}

Guarding Against Recursive Structures

import reprlib


class Node:
    def __init__(self):
        self.child = None

    @reprlib.recursive_repr("<...>")
    def __repr__(self):
        return f"Node({self.child!r})"


node = Node()
node.child = node  # a cycle: without the decorator this recurses forever

print(repr(node))
# Node(<...>)