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Python Style Guide from Google

Google Python Style Guide

Revision 2.59

Amit Patel

Antoine Picard

Eugene Jhong

Jeremy Hylton

Matt Smart

Mike Shields

Each style point has a summary for which additional information is available by toggling the accompanying arrow button that looks this way: . You may toggle all summaries with the big arrow button:

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Table of Contents

Python Language Rules

Nested/Local/Inner Classes and Functions Default Iterators and Operators Conditional Expressions Default Argument Values True/False evaluations Deprecated Language Features Function and Method Decorators

Important Note

Displaying Hidden Details in this Guide

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This style guide contains many details that are initially hidden from view. They are marked by the triangle icon, which you see here on your left. Click it now. You should see "Hooray" appear below.

Background

Python is the main scripting language used at Google. This style guide is a list of do s and don’t s for Python programs.

To help you format code correctly, we’ve created a settings file for Vim . For Emacs, the default settings should be fine.

Python Language Rules

Lint

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Run pylint over your code.

Imports

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Use import s for packages and modules only.

Packages

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

Exceptions

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Exceptions are allowed but must be used carefully.

Global variables

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Avoid global variables.

Nested/Local/Inner Classes and Functions

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Nested/local/inner classes and functions are fine.

List Comprehensions

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Okay to use for simple cases.

Default Iterators and Operators

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

Generators

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Use generators as needed.

Lambda Functions

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Okay for one-liners.

Conditional Expressions

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Okay for one-liners.

Default Argument Values

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Okay in most cases.

Properties

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

True/False evaluations

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Use the "implicit" false if at all possible.

Deprecated Language Features

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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

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Okay to use.

Function and Method Decorators

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Use decorators judiciously when there is a clear advantage.

Threading

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

Power Features

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Avoid these features.

Python Style Rules

Semicolons

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

Line length

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Maximum line length is 80 characters .

Parentheses

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Use parentheses sparingly.

Indentation

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Indent your code blocks with 4 spaces .

Blank Lines

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

Whitespace

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

Shebang Line

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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

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

Classes

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

Strings

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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

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Explicitly close files and sockets when done with them.

TODO Comments

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

Imports formatting

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Imports should be on separate lines.

Statements

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Generally only one statement per line.

Access Control

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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

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Main

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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.

Revision 2.59

Amit Patel

Antoine Picard

Eugene Jhong

Gregory P. Smith

Jeremy Hylton

Matt Smart

Mike Shields

Shane Liebling

转载本站任何文章请注明:转载至神刀安全网,谢谢神刀安全网 » Python Style Guide from Google

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