Automate Python Code Review Using Flake8

What is a Code Review?

Code review is a systematic process in which developers examine source code written by their peers to ensure quality, consistency, and adherence to best practices. The primary goal of code review is to identify bugs, logical errors, and inefficiencies.

What is Flake8?

Flake8 enhances the code review process by automating many of the checks that would otherwise need to be performed manually. It helps identify and flag code that does not adhere to PEP8, as well as potential errors, stylistic inconsistencies, and complex code that may need simplification.

Flake8 is a comprehensive tool that acts as a linter for Python projects. Unlike a formatter such as Black, which directly alters your code’s structure, Flake8 highlights issues and lets you decide how to address them.

How to Use Flake8?

1. Activate your virtual environment

Before installing Flake8, you have to activate your virtual environment. A virtual environment helps isolate your project's dependencies from your global Python installation.

2. Install Flake8 via pip

Once your virtual environment is active, download and install Flake8 using pip by entering the following command in your terminal:

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pip install flake8

3. Flag codes to be ignored

You may want to flag the code that Flake8 should not check on.

To ignore a single line of code, use # noqa:

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def messy_function(x,y):
  if x>y: print("X is greater than Y") # noqa
  else:
        print("Y is greater or equal to X")

To ignore the entire file, use # flake8: noqa:

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# flake8: noqa

def messy_function(x,y):
  if x>y: print("X is greater than Y")
  else:
        print("Y is greater or equal to X")

To ignore a list of files, use the following code in your terminal:

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flake8 --exclude=sample_1.py,sample_2.py

You can also include this in your configuration file as:

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[flake8]
exclude = sample_1.py,sample_2.py

4. (Optional) Customize Flake8's configuration

To customize Flake8's behavior, you can use configuration files, such as setup.cfg, tox.ini, or .flake8. For more information, you may want to visit Flake8's official documentation on its supported config files.

I prefer to use the .flake8 file as it is easy to understand that this configuration file is related to Flake8.

Using the Gen EMR project as an example, below is a sample production .flake8 file for our Django project. This configuration is needed to make Flake8 compatible with Black.

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[flake8]
max-line-length = 80
extend-select = B950
extend-ignore = E203,E501,E701

You may want to view the Flake8's available config options.

• The max-line-length enforces a maximum line length of 80 characters.
• The extend-select flags overly long lines as errors but allows some leniency beyond the max-line-length.
• The extend-ignore ignores specific warnings or errors: E203 (whitespace before :), E501 (line too long), and E701 (multiple statements on one line).

Take Note: It is recommended to install the Bugbear plugin when integrating Flake8 with Black.

In the last section of this tutorial, check out the sample output using this configuration.

5. Check Files

Make sure to navigate to your source code directory before running the following code.

To check a single file:

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flake8 [file_name].py

To format the files in the entire directory:

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flake8 [directory_name]/

Sample Flake8's Checking

Python code:

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def messy_function(x,y):
  if x>y: print("X is greater than Y")
  else:
        print("Y is greater or equal to X")

Terminal output:

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sample/sample.py:1:21: E231 missing whitespace after ','
sample/sample.py:2:3: E111 indentation is not a multiple of 4
sample/sample.py:2:7: E225 missing whitespace around operator
sample/sample.py:3:3: E111 indentation is not a multiple of 4
sample/sample.py:4:9: E117 over-indented