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This is style50, a tool with which code can be checked against the CS50 style guide.


pip install style50

In order to style check C, C++, or Java code, a recent version (>=14.0.0) of clang-format must be installed. clang-format may be downloaded here.


Along with most of CS50's command line tools, style50 supports being run on Windows but only via the Linux Subsystem in Windows 10. After launching it, style50 can be installed using the pip command above.


usage: style50 [-h] [-o MODE] [-v] [-V] [-E] [-i PATTERN] file [file ...]

positional arguments:
file                  file or directory to lint

optional arguments:
-h, --help            show this help message and exit
-o MODE, --output MODE
                        output mode, which can be character (default), split,
                        unified, score, or json
-v, --verbose         print full tracebacks of errors
-V, --version         show program's version number and exit
-E, --extensions      print supported file extensions (as JSON list) and
-i PATTERN, --ignore PATTERN
                        paths/patterns to be ignored

character, split, and unified modes output character-based, side-by-side, and unified (respectively) diffs between the inputted file and the correctly styled version. score outputs the raw percentage of correct (unchanged) lines, while json outputs a json object containing information pertinent to the CS50 IDE plugin (coming soon).

Language Support

style50 currently supports the following languages:

  • C++
  • C
  • Python
  • Javascript
  • Java

Adding a new language

Adding a new language is very simple. Language checks are encoded as classes which inherit from the StyleCheck base class (see style50/ for more real-world examples). The following is a template for style checks which allows style50 to check the imaginary FooBar language for style.

import re

from style50 import StyleCheck, Style50

class FooBar(StyleCheck):

    # REQUIRED: this property informs style50 what file extensions this
    # check should be run on (in this case, all .fb and .foobar files)
    extensions = ["fb", "foobar"]

    # REQUIRED: should return a correctly styled version of `code`
    def style(self, code):
        # All FooBar code is perfectly styled
        return code

    # OPTIONAL: should return the number of comments in `code`.
    # If this function is not defined, `style50` will not warn the student about
    # too few comments
    def count_comments(self, code):
        # A real-world, check would need to worry about not counting '#' in string-literals
        return len(re.findall(r"#.*", code))

All classes which inherit from StyleCheck are automatically registered with style50's Style50 class, making style50 easily extensible. Adding the following to the above code creates a script which checks the code that style50 already does as well as FooBar programs.

    # Style check the current directory, printing a unified diff