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Python Coding Convention

Got curious about PEP8, so I looked it up and decided to organize it

References: [Book] Effective Python



What is PEP8?

Python Enhancement Proposal 8 (PEP8)

  • A style guide that tells you how to organize Python code
    • An agreement to write code in a specific format
      • Using a consistent style makes maintenance easier and improves readability!
  • Detailed information is available at python.org!


Some Rules from PEP8 That Must Be Followed


1. Whitespace

In Python, whitespace is syntactically significant

Python programmers are particularly sensitive to the impact of whitespace because of code clarity!

  • Indent with spaces, not tabs

  • Use 4 spaces for each level of syntactically significant indentation

  • Each line should be 79 characters or less

  • When an expression continues to the next line, use 4 additional spaces beyond the normal indentation level

  • Functions and classes in a file should be separated by two blank lines

  • Methods within a Class should be separated by a single blank line

  • Do not use spaces around list indices, function calls, or keyword argument assignments


2. Naming Conventions

PEP 8 suggests unique naming conventions for different parts of the language

This makes it easy to distinguish the type corresponding to each name when reading code!

  • Functions, variables, and attributes follow the lowercase_underscore format
  • Protected instance attributes follow the _leading_underscore format
  • Private instance attributes follow the __double_leading_underscore format
  • Classes and Exceptions follow the CapitalizedWord format
  • Module-level constants follow the ALL_CAPS format
  • The first parameter of a Class instance method (which references the object) should be named self
  • The first parameter of a Class method (which references the class) should be named cls

3. Expressions and Statements

The Zen of Python states: "There should be one-- and preferably only one --obvious way to do it"

PEP 8 codifies this style as the standard for expressions and statements

  • Use inline negation (if a is not b) instead of negation of positive expressions (if not a is b)
  • Don't check for empty values ([] or '') by checking the length (if len(somelist) == 0)
    • Use if not somelist and assume that empty values are implicitly False
    • The same approach applies to non-empty values!
      • Non-empty values will make if somelist implicitly True
  • Don't write single-line if statements, for and while loops, or except compound statements
    • Write these statements on multiple lines for clarity!
  • Always place import statements at the top of the file
  • When importing modules, always use the module's absolute name; do not use relative path names based on the current module's path
    • ex) Use from bar import foo instead of just import foo!
  • If you must use relative imports, use explicit syntax: from . import foo
  • Imports should be organized in the order of standard library modules, third-party modules, and your own modules
    • Within each subsection, import in alphabetical order


How to Check If You're Following PEP8

Install and use pylint and PEP8!


1. pylint

$ pip install pylint

2. PEP8

$ pip install pep8