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Static Python code analyzer, that tries to check if functions in code are pure or not and why.

Project description

mr. Proper

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Static Python code analyzer, that tries to check if functions in code are pure or not and why.

Have fun with mr Clean

DISCLAIMER: this library is very experimental and has a lot of edge cases. Functions that mr. Proper marks as pure can be not pure, but they are usually cleaner than other functions.


pip install mr_proper

What mr. Proper check

  1. that function has no blacklisted calls (like print) and blacklisted attributes access (like smth.count);
  2. that function not uses global objects (only local vars and function arguments);
  3. that function has al least one return;
  4. that function not mutates it's arguments;
  5. that function has no local imports;
  6. that function has no arguments of forbidden types (like ORM objects);
  7. that function not uses self, class or super;
  8. that function has calls of only pure functions.

This list is not enought to say that function is pure and some points are quite controversial, but it's a nice start.


Console usage:

    def add_one(n: int) -> int:
        return n + 1

    def print_amount_of_users(users_qs: QuerySet) -> None:
        print(f'Current amount of users is {users_qs.count()}')
$ mr_propper
add_one is pure!
print_amount_of_users is not pure because of:
    it uses forbidden argument types (QuerySet)
    it calls not pure functions (print)
    it has no return

Usage inside Python code sample:

>>> import ast
>>> from mr_propper.utils import is_function_pure
>>> funcdef = ast.parse('''
    def add_one(n: int) -> int:
        return n + 1
>>> is_function_pure(funcdef)
>>> is_function_pure(funcdef, with_errors=True)
(True, [])


CLI interface:

  • filepath: path to .py file to check (directories are not supported for now);
  • --recursive: require inner calls to be pure for function pureness.

Code prerequisites

  1. Python 3.7+;
  2. Functions are fully type-annotated;
  3. No dynamic calls (like getattr(sender, 'send_' + message_type)(message)).


We would love you to contribute to our project. It's simple:

  1. Create an issue with bug you found or proposal you have. Wait for approve from maintainer.
  2. Create a pull request. Make sure all checks are green.
  3. Fix review comments if any.
  4. Be awesome.

Here are useful tips:

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