re-assert

1.1.0 verified Mon Apr 27 auth: no python

A library to show where your regex match assertion failed. It provides a helper to clarify regex failures in tests. Current version: 1.1.0, release cadence: low, maintained by asottile.

pip install re-assert

Common errors

error ImportError: cannot import name 're_assert' ↓

cause Incorrect import: the module is named re_assert (with underscore), not re-assert (with hyphen).

fix

Use 'from re_assert import ReAssert' (note underscore)

error AttributeError: module 're_assert' has no attribute 'ReAssert' ↓

cause Version mismatch or incorrect installation. Ensure package is installed as 're-assert'.

fix

Run 'pip install re-assert' and import with 'from re_assert import ReAssert'

error TypeError: 'ReAssert' object is not callable ↓

cause Attempting to call ReAssert as a function. It is a class, instantiate it first.

fix

matcher = ReAssert(pattern); then matcher == 'string'

Warnings

gotcha ReAssert uses __eq__ to perform matching. Ensure you are comparing the ReAssert object to a string, not the other way around. ↓

fix Use 'matcher == string' pattern.

gotcha The library is designed for testing; it does not raise exceptions but returns False and prints diagnostic info. Do not use it for production regex validation without assertions. ↓

fix Use in test suites with pytest or unittest.

Imports

ReAssert
```
from re_assert import ReAssert
```
ReAssert is the main class for assertion with better error messages.

Quickstart

Basic usage: create a ReAssert object with a regex pattern, then compare with a string. If match fails, it prints where and why.

from re_assert import ReAssert

# Pattern with group names
pattern = r"(?P<name>\w+) (?P<age>\d+)"
matcher = ReAssert(pattern)

# This assertion will fail with a detailed message
# matcher == 'John 30 extra'
# Uncomment to see error: matcher == 'John 30' (this matches)