Exrex

0.12.0 · active · verified Thu Apr 16

Exrex is a Python library and command-line tool for 'reverse regular expressions,' designed to generate strings that match a given regular expression. It's useful for tasks like testing, fuzzing, and creating sample data. The library supports common regex features and handles potentially infinite matching strings by limiting their maximum length. It is a pure Python library with no external dependencies and efficiently uses generators to manage memory. The current version is 0.12.0, with an infrequent release cadence.

Common errors

```
ModuleNotFoundError: No module named 'exrex'
```
cause The `exrex` library has not been installed in your current Python environment.

fix Run `pip install exrex` in your terminal to install the package.
```
TypeError: 'generator' object is not subscriptable
```
cause You are trying to access elements from the `exrex.generate()` function directly using an index (e.g., `exrex.generate('...')[0]`) instead of iterating over it or converting it to a list.

fix Convert the generator to a list if you need random access (e.g., `list(exrex.generate('...'))`) or iterate through it (e.g., `for s in exrex.generate('...'): print(s)`).
```
exrex.py: error: argument REGEX: invalid regex
```
cause This error occurs when using `exrex` from the command line, indicating that the provided regular expression string is syntactically invalid or not correctly escaped for your shell.

fix Ensure your regular expression is correctly formatted. If it contains special shell characters, enclose it in appropriate quotes (single quotes are usually safer on Unix-like systems, double quotes on Windows). Test the regex with Python's `re` module or an online regex validator first.

Warnings

gotcha Generating all possible strings for complex or broad regular expressions can consume significant memory and time. Use the `limit` parameter (e.g., in `generate` or `count`) or prefer `getone` for efficiency, especially with infinite patterns like `.*` or `[a-z]+`.
Fix: Always consider the potential output size. For `generate`, wrap in `list()` with caution, or iterate directly. Use `exrex.getone()` for a single random match. For patterns with quantifiers like `+` or `*`, `exrex` applies an internal limit to generated length to prevent infinite loops and excessive output, but this may not cover all memory/performance implications.
deprecated While PyPI classifiers for `exrex` list compatibility with Python 2.6, 2.7, and Python 3.3-3.5, these versions are officially end-of-life and unsupported. Relying on `exrex` with these older Python versions may lead to unpatched issues or compatibility problems with other modern libraries.
Fix: It is strongly recommended to use `exrex` with Python 3.6 or newer for better security, performance, and compatibility within modern Python environments. The library explicitly states Python 3.3+ compatibility, but best practice suggests newer Python 3 versions.
gotcha The `exrex` library may not fully support all advanced or obscure features of Python's `re` module. While it handles most common regex patterns, certain complex constructs or specific flags might behave unexpectedly or not be fully implemented, leading to parsing errors or incorrect string generation.
Fix: Test `exrex` with your specific complex regex patterns to ensure desired behavior. Consult the library's GitHub issues for known limitations or open a new issue if you encounter unexpected behavior with a standard regex pattern.

Install

pip install exrex Install latest version

Imports

exrex
```
import exrex
```
The primary module is typically imported directly.
generate
wrong:
```
import exrex.generate
```
correct:
```
from exrex import generate
```
Functions like 'generate' are members of the exrex module, not submodules.

Quickstart

The quickstart demonstrates generating a single random string, iterating through all possible matching strings (up to an internal limit for infinite regexes), and counting the total number of matches for a given regular expression.

import exrex

# Generate a single random string matching a regex
random_string = exrex.getone('[a-z]{3}\d{2,4}')
print(f"Random string: {random_string}")

# Generate all matching strings for a simple regex (up to a default limit)
all_strings = list(exrex.generate('(hello|world)!'))
print(f"All strings: {all_strings}")

# Count the number of matching strings
count = exrex.count('[01]{0,3}')
print(f"Count of [01]{0,3} matches: {count}")

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