Introduction

pysource_codegen is able to generate random python code which can be compiled. The compiled code should not be executed.

This is still a very early version, but it does its job. It is general useful to test tools like formatters, linters or anything which operates on python code.

Install:

pip install pysource-codegen

Usage:

The tool can be used over the CLI:

pysource-codegen --seed 42

or as a library:

from pysource_codegen import generate

seed = 42
print(generate(seed))

You might find pysource-minimize also useful to reduce the generated code which triggers your bug down to a minimal code snipped, which can be used to fix the issue.

from pysource_codegen import generate
from pysource_minimize import minimize


def contains_bug(code):
    """
    returns True if the code triggers a bug and False otherwise
    """
    try:
        test_something_with(code)  # might throw

        if "bug" in code:  # maybe other checks
            return True
    except:
        return True
    return False


def find_issue():
    for seed in range(0, 10000):
        code = generate(seed)

        if contains_bug(code):
            new_code = minimize(code, contains_bug)

            print("the following code triggers a bug")
            print(new_code)

            return


find_issue()

Bugs found in other projects:

black

• https://github.com/psf/black/issues/3676
• https://github.com/psf/black/issues/3678
• https://github.com/psf/black/issues/3677

cpython

• https://github.com/python/cpython/issues/109219
• https://github.com/python/cpython/issues/109823
• https://github.com/python/cpython/issues/109719
• https://github.com/python/cpython/issues/109627
• https://github.com/python/cpython/issues/109219
• https://github.com/python/cpython/issues/109118
• https://github.com/python/cpython/issues/109114

Todo:

• refactor the existing code
• use probabilities for the ast-nodes from existing python code (use markov chains)
• support older python versions
• allow to customize the probabilities to generate code to test specific language features
• hypothesis support