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https://github.com/isidentical/refactor

AST-based fragmental source code refactoring toolkit for Python
https://github.com/isidentical/refactor

ast python refactoring

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AST-based fragmental source code refactoring toolkit for Python

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README 

        
# Refactor



[![PyPI version](https://badge.fury.io/py/refactor.svg)](https://badge.fury.io/py/refactor)

[![Documentation](https://img.shields.io/badge/%3D%3E-Documentation-brightgreen)](https://refactor.readthedocs.io)

[![Try It](https://img.shields.io/badge/Try%20It-getrefactor.com-green?style=for-the-badge)](https://getrefactor.com)



Simple, hassle-free, dependency-free, AST based fragmental source code refactoring

and transformation toolkit.



## Why?



Our framework is primarily built on the principle of "simple but effective

transformations". We focus on refactorings that target a small span of

source code, and work our way out from it. What this enables for us is

being able to operate directly on a single format for both analyses and

transformations. This is what we shine at compared to other similar tools.



## How?



Let's not get into too much details, but just to give a sneak peek we

can try to write a rule that would replace the identifier `placeholder`

with `42`.



```py

import ast

from refactor import Rule, Replace, run



# Each refactor transformer inherits from "refactor.Rule"

class FillPlaceholders(Rule):



    # And each rule implements a "match()" method, which would

    # receive every node in the tree in a breadth-first order.

    def match(self, node: ast.AST) -> Replace:

        # This is where things get interesting. Instead of just writing

        # filters with if statements, you can use the following assert

        # based approach (a contract of transformation).



        # For this case, our contract is going to be: if the given node

        # is an identifier with the name of "placeholder", it will be

        # replaced with literal "42".

        assert isinstance(node, ast.Name)

        assert node.id == "placeholder"



        # And this is where we choose what action we are taking for the

        # given node (which we have verified with our contract). There

        # are multiple transformation actions, but in this case what we

        # need is something that replaces a node with another one.

        replacement = ast.Constant(42)

        return Replace(node, replacement)



if __name__ == "__main__":

    # And finally in here, we just use the default CLI that comes

    # bundled with refactor. When provided with a bunch of rules,

    # it creates a simple interface that can process given files

    # show the diff for changes and even apply them.

    run(rules=[FillPlaceholders])

```



If we run the rule above on a file, we can see how it performs:



```diff

--- test_file.py

+++ test_file.py



@@ -1,11 +1,11 @@



def main():

-    print(placeholder * 3 + 2)

+    print(42 * 3 + 2)

-    print(2 +               placeholder      + 3)

+    print(2 +               42      + 3)

     # some comments

-    placeholder # maybe other comments

+    42 # maybe other comments

     if something:

         other_thing

-    print(placeholder)

+    print(42)



if __name__ == "__main__":

     main()

```



For learning more, check our [documentation](https://refactor.readthedocs.io/en/latest/) out!