Format Python code correctly the Google way!

Posted on Updated on

This style guide from google can help clean up your code and bring you up to speed on sharing your work with others and easily understanding other’s work

Background

Python is the main scripting language used at Google. This style guide is a list of dos and don’ts for Python programs.

.

Python Language Rules

Lint

Run pylint over your code.

Imports

Use imports for packages and modules only.

Packages

Import each module using the full pathname location of the module.

Exceptions

Exceptions are allowed but must be used carefully.

Global variables

Avoid global variables.

Nested/Local/Inner Classes and Functions

Nested/local/inner classes and functions are fine.

List Comprehensions

Okay to use for simple cases.

Default Iterators and Operators

Use default iterators and operators for types that support them, like lists, dictionaries, and files.

Generators

Use generators as needed.

Lambda Functions

Okay for one-liners.

Conditional Expressions

Okay for one-liners.

Default Argument Values

Okay in most cases.

Properties

Use properties for accessing or setting data where you would normally have used simple, lightweight accessor or setter methods.

True/False evaluations

Use the “implicit” false if at all possible.

Deprecated Language Features

Use string methods instead of the string module where possible. Use function call syntax instead of apply. Use list comprehensions and for loops instead of filter and map when the function argument would have been an inlined lambda anyway. Use for loops instead of reduce.

Lexical Scoping

Okay to use.

Function and Method Decorators

Use decorators judiciously when there is a clear advantage.

Threading

Do not rely on the atomicity of built-in types.

Power Features

Avoid these features.

Python Style Rules

Semicolons

Do not terminate your lines with semi-colons and do not use semi-colons to put two commands on the same line.

Line length

Maximum line length is 80 characters.

Parentheses

Use parentheses sparingly.

Indentation

Indent your code blocks with 4 spaces.

Blank Lines

Two blank lines between top-level definitions, one blank line between method definitions.

Whitespace

Follow standard typographic rules for the use of spaces around punctuation.

Shebang Line

Most .py files do not need to start with a #! line. Start the main file of a program with #!/usr/bin/python with an optional single digit 2 or 3 suffix per PEP-394.

Comments

Be sure to use the right style for module, function, method and in-line comments.

Classes

If a class inherits from no other base classes, explicitly inherit from object. This also applies to nested classes.

Strings

Use the format method or the % operator for formatting strings, even when the parameters are all strings. Use your best judgement to decide between + and % (or format) though.

Files and Sockets

Explicitly close files and sockets when done with them.

TODO Comments

Use TODO comments for code that is temporary, a short-term solution, or good-enough but not perfect.

Imports formatting

Imports should be on separate lines.

Statements

Generally only one statement per line.

Access Control

If an accessor function would be trivial you should use public variables instead of accessor functions to avoid the extra cost of function calls in Python. When more functionality is added you can use property to keep the syntax consistent.

Naming

module_name, package_name, ClassName, method_name, ExceptionName, function_name, GLOBAL_CONSTANT_NAME, global_var_name, instance_var_name, function_parameter_name, local_var_name.

Main

Even a file meant to be used as a script should be importable and a mere import should not have the side effect of executing the script’s main functionality. The main functionality should be in a main() function.

Parting Words

BE CONSISTENT.

If you’re editing code, take a few minutes to look at the code around you and determine its style. If they use spaces around all their arithmetic operators, you should too. If their comments have little boxes of hash marks around them, make your comments have little boxes of hash marks around them too.

The point of having style guidelines is to have a common vocabulary of coding so people can concentrate on what you’re saying rather than on how you’re saying it. We present global style rules here so people know the vocabulary, but local style is also important. If code you add to a file looks drastically different from the existing code around it, it throws readers out of their rhythm when they go to read it. Avoid this.

https://google.github.io/styleguide/pyguide.html

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s