flake8-no-private-methods

flake8-no-private-methods is a Flake8 plugin that prohibits the use of private methods in Python code. The plugin is based on the object-oriented programming principle: each private method is a candidate for a new class.

Each Private Static Method Is a Candidate for a New Class

Installation

Install flake8-no-private-methods via pip:

pip install flake8-no-private-methods

Usage

To use flake8-no-private-methods, simply include it in your Flake8 configuration. Run Flake8 as usual, and the plugin will check for the presence of private methods in your code.

flake8 your_code_directory

Example

Problematic code

class Token:
    def __init__(self, key, secret):
        self.key = key
        self.secret = secret
    
    def encoded(self):
        return "key=" + self._encode(self.key) + "&secret=" + self._encode(self.secret)
    
    def _encode(self, text):  # Private method - violation!
        return URLEncoder.encode(text, "UTF-8")

Running flake8 will produce the following error:

your_file.py:8:4: NPM100 private methods forbidden

Correct code

Instead of a private method, create a separate class:

class Encoded:
    def __init__(self, raw):
        self.raw = raw
    
    def __str__(self):
        return URLEncoder.encode(self.raw, "UTF-8")

class Token:
    def __init__(self, key, secret):
        self.key = key
        self.secret = secret
    
    def encoded(self):
        return "key=" + str(Encoded(self.key)) + "&secret=" + str(Encoded(self.secret))

Rationale

Private methods in Python reduce code modularity, testability, and reusability. The main problems with private methods:

• Not reusable: private methods cannot be used in other classes
• Not testable: it's difficult to create unit tests for private methods
• Violate single responsibility principle: a class takes on too many responsibilities

The flake8-no-private-methods plugin encourages developers to create separate classes instead of private methods, which leads to:

• Better modularity: each class has a single responsibility
• Improved testability: each class can be tested independently
• Enhanced reusability: functionality can be used in different places
• Cleaner design: code becomes more object-oriented

As Yegor Bugayenko said: "Each private method is a candidate for a new class".

License

MIT

Credits

This project was generated with wemake-python-package. Current template version is: 864a62ecb432655249d071e263ac51f053448659. See what is updated since then.

The plugin idea is based on Yegor Bugayenko's article about how each private method is a candidate for a new class.