Pycharm + Black with Formatting on Auto-save

So, lately, I’ve been working with Black for Python code formatting. Pretty cool huh!

I’ve seen Black do wonders to my code. It made my (already pretty) code look prettier, I could just gawk at it for hours. But, running black on every file became a tedious task as the size of the project grew. This triggered an urge to find a way to run black as soon as the file is saved.

Here, I’m presenting a way to do that with Pycharm on MacOS.

Firstly, install black in your virtualenv if not already done.

$ pip install black

You can as well install the package from pycharm preferences.

• Pycharm > Preferences
• Search for Python Interpreter
• Click on the “+” icon and type “Black”
• Click on install package

Once you’ve installed Black, click Apply and OK.

You need to open the Preferences again. This time search for External tools.

• Preference > Tools > External Tools
• Click on the “+” icon
• Mention your desired Name in the Name input, and give it some description.
• In tool settings, update as following

Programs: $PyInterpreterDirectory$/black
Arguments: $FilePath$
Working directory: $ProjectFileDir$

• Click on “OK”

Now, you’ve done the basic setup of Black and you can now format any file by going on Tools > External Tools ( Your Group name, mine is Black) > Black.

But wait, if we have to do it for every file, then how does it solve the problem, where is the functionality to run black on auto-save.

Hold your Horses…

We need to go to preferences yet again, I promise this will be the last time.

• Preferences > Search “File Watchers”
• Under Tools > File Watchers > Click on the “+” icon.
• Select “custom”

In the dialog box which appears,

• Input Name of your choosing in “Name”
• In File type select “Python”
• In ‘tool to run on changes’ input following

Program: $PyInterpreterDirectory$/black
Arguments: $FilePath$
Output paths to refresh: $FilePath$
Working directory: $ProjectFileDir$

Click on “OK” and you’re good to go.

Now just restart your Pycharm instance and you can witness the “Black” magic.

Cheers 🥂