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Material for the course "Python best practices", Scientific Software Center, Heidelberg University

Code formatter

A code formatter takes care of formatting your code so that it adheres to the styling standards. For Python, a popular code formatter is black. Black is PEP 8 compliant but also adds some own flavor to the code. Comparing code that has been formatted with black makes it easier to spot the differences. You can even try it out online.

You first need to install black using

pip install black

You can then use black running it as

black Material_Part3_Formatter/

Please note that the formatter reformats the file in-place, that means, substituting the content of the original file!

Now you can check with flake8 if the file is compliant with PEP 8:

flake8 Material_Part3_Formatter/

You will notice that flake8 is not returning errors except a line length error for one of the comment lines: Note that black does not reformat comments other than inserting proper whitespace before and after the #.

Task 1: Reformat and using black. Compare to your own reformatted files.

Black configuration

Sometimes you only want to check what black would actually reformat. In order to do so, run

black Material_Part3_Formatter/ --diff


black Material_Part3_Formatter/ --diff --color

Task 2: Try this out with your own reformatted files from Part 1 of this course (PEP style guide).

Black with jupyter notebooks

The new versions of black directly allow you to run it on jupyter notebooks,

Task 3: Try out reformatting notebooks with this example.

Black with VSCode

If you are using an IDE, specifically Visual Studio Code, you can set up black as the default formatter for your *.py files. Follow the instructions provided here.

For more tips and tricks, see this page.