Python pylint

What is pylint?

pylint is a static code analyzer that checks Python source code for errors, enforces coding standards, and suggests improvements for readability and maintainability.

How to Install pylint

Install pylint using pip:

pip install pylint

Verify installation:

pylint --version

How to Use pylint

1. Run pylint on a Python script or module:

   pylint your_script.py

2. Read the output report, which includes:
   • Errors (e.g., syntax issues)
   • Warnings (e.g., unused imports, variables)
   • Refactor suggestions
   • Convention violations (e.g., naming style)
3. Fix issues or decide which warnings to ignore.
4. Optionally, customize behavior with a .pylintrc config file.

Common pylint Rules

pylint categorizes messages by type and provides specific message codes. Here are some common categories and examples:

• Convention (C): Coding standard violations
  • C0103 - Invalid naming style (e.g., variable or function name not snake_case)
  • C0114 - Missing module docstring
  • C0115 - Missing class docstring
• Refactor (R): Suggestions for code improvements
  • R0913 - Too many arguments in function
  • R1705 - Simplify conditional expression
• Warning (W): Possible errors or suspicious code
  • W0611 - Unused import
  • W0612 - Unused variable
• Error (E): Syntax or runtime errors
  • E1101 - Module has no member (possible typo or wrong import)
  • E0001 - Syntax error
• Fatal (F): Serious errors that prevent pylint from running
  • F0001 - Fatal error (e.g., invalid Python version)

Example 1: Basic pylint Check

# bad_script.py
def myFunction():
print("Hello")  # Indentation error and naming style warning

Running pylint bad_script.py highlights errors and warnings.

Example 2: Ignoring a Warning with a Comment

def foo():
    x = 1  # pylint: disable=unused-variable
    print("Foo called")

This disables the warning about the unused variable x for that line.

Example 3: Configuring pylint with a .pylintrc File

[MESSAGES CONTROL]
disable=C0114, C0115, C0116  # disable missing docstring warnings

Place this file in your project root to customize pylint's checks globally.

Using pylint regularly helps maintain clean, readable, and error-free Python code.