README.md
# mr. Proper
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Static Python code analyzer, that tries to check if functions in code are
[pure](https://en.wikipedia.org/wiki/Pure_function) or not and why.
![Have fun with mr Clean](https://raw.githubusercontent.com/best-doctor/mr_proper/master/docs_img/mr_clean_sponge.jpg)
*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.
## Installation
```bash
pip install mr_proper
```
## What mr. Proper check
1. that function has no blacklisted calls (like `print`)
and blacklisted attributes access (like `smth.count`);
1. that function not uses global objects (only local vars and function arguments);
1. that function has al least one return;
1. that function not mutates it's arguments;
1. that function has no local imports;
1. that function has no arguments of forbidden types (like ORM objects);
1. that function not uses `self`, `class` or `super`;
1. that function has calls of only pure functions.
This list is not enough to say that function is pure and some points
are quite controversial, but it's a nice start.
## Example
Console usage:
```python
# test.py
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()}')
```
```bash
$ mr_propper test.py
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:
```jupyterpython
>>> import ast
>>> from mr_propper.utils import is_function_pure
>>> funcdef = ast.parse('''
def add_one(n: int) -> int:
return n + 1
''').body[0]
>>> is_function_pure(funcdef)
True
>>> is_function_pure(funcdef, with_errors=True)
(True, [])
```
## Parameters
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+;
1. Functions are fully type-annotated;
1. No dynamic calls (like `getattr(sender, 'send_' + message_type)(message)`).
## Contributing
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.
1. Create a pull request. Make sure all checks are green.
1. Fix review comments if any.
1. Be awesome.
Here are useful tips:
- You can run all checks and tests with `make check`.
Please do it before TravisCI does.
- We use [BestDoctor python styleguide](https://github.com/best-doctor/guides/blob/master/guides/en/python_styleguide.md).
- We respect [Django CoC](https://www.djangoproject.com/conduct/).
Make soft, not bullshit.