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Python Time & Space Complexity

Doctest

doctest Module¶

The doctest module finds and runs tests embedded in docstrings. It extracts example code from docstrings and verifies the output matches.

Complexity Reference¶

Operation	Time	Space	Notes
`doctest.testmod()`	O(n)	O(n)	n = docstring lines
Example extraction	O(n)	O(n)	Parse docstrings
Test execution	O(k)	O(1)	k = number of examples

Running Doctests¶

Basic Doctest¶

import doctest

def add(a, b):
    """
    Add two numbers.

    >>> add(2, 3)
    5
    >>> add(-1, 1)
    0
    """
    return a + b

# Run tests - O(n) where n = docstring examples
doctest.testmod(verbose=True)
# Trying: add(2, 3)
# Expecting: 5
# ok

Testing with Output¶

import doctest

def greet(name):
    """
    Greet someone.

    >>> greet('Alice')
    'Hello, Alice!'
    >>> greet('Bob')
    'Hello, Bob!'
    """
    return f"Hello, {name}!"

# Test - O(n)
results = doctest.testmod()
print(f"Tests: {results.attempted}, Failures: {results.failed}")

Running Doctests on Modules¶

Module-Level Testing¶

import doctest
import mymodule

# Run all doctests in module - O(n)
doctest.testmod(mymodule, verbose=True)

# Or from command line:
# python -m doctest mymodule.py -v