Effective Python: 2 Follow the PEP 8 Style Guide

Python Enhancement Proposal (PEP) #8 is the style guide for how to format Python code. Here are a few rules we should be sure to follow!

1. Whitespace

• Use spaces instead of tabs for indentation.
• Use four spaces for each level of significant indenting.
• Lines should be 79 characters in length or less.
• Additional lines should be indented by four extra spaces from their normal indentation level.
• In a file, functions and classes should be separated by two blank lines.
• In a class, methods should be separated by one blank line.
• In a dictionary, put no whitespace between each key and colon, and put a single space before the corresponding value if it fits on the same line.
• Put one space before and after the = operator in a variable assignment.
• For type annotations, ensure that there is no separation between the variable name and the colon, and use a space before the type information.

2. Naming

• Functions, variables, and attributes should be in lowercase_underscore format.
• Protected instance attributes should be in _leading_undersocre format.
• Private instance attributes should be in __double_leading_underscore format.
• Classes (including exceptions) should be in CapitalizedWord format.
• Module-level constants should be in ALL_CAPS format.
• Instance methods in classes should use self, which refers to the object, as the name of the first parameter.
• Class methods should use cls, which refers to the class, as the name of the first parameter.

3. 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 containers or sequences (like [] or ‘’) by comparing the length to zero (if len(some_list) == 0). Use if not some_list and assume that empty values will implicitly evaluate to False.
• The same thing goes for non-empty containers or sequences.
• Avoid single-line if statements, for and while loops, and except compound statements.
• If you can’t fit an expression on one line, surround it with parentheses and add line breaks and indentation to make it easier to read.
• Prefer surrounding multiline expressions with parentheses over using the \ line continuation character.

4. Imports

• Always put import statements at the top of a file.
• Always use absolute names for modules when importing them.
• If you must do relative imports, use the explicit syntax.
• Imports should be in sections in the following order: standard library modules, third-party modules, and your modules.

[embed]Two ways to import module