python 代码格式化工具：autopep8

学习资料： https://github.com/hhatto/autopep8 

背景

autopep8 会根据 PEP 8 样式文档来格式化 python 代码。它使用 pep8 来决定代码的哪部分需要被格式化。 autopep8 可以修复 pep8汇报的大部分格式问题。

PEP8 是 Python Enhancement Proposal 的缩写，翻译过来就是 python 增强建议书， 是python的一个官方样式指导。它规定了一些比较好的编码方式，比如用4个空格代替缩进等等。

PEP 0008 -- Style Guide for Python Code： https://www.python.org/dev/peps/pep-0008/

安装

$ pip install --upgrade autopep8

用法

usage: autopep8 [-h] [--version] [-v] [-d] [-i] [--global-config filename]
                [--ignore-local-config] [-r] [-j n] [-p n] [-a]
                [--experimental] [--exclude globs] [--list-fixes]
                [--ignore errors] [--select errors] [--max-line-length n]
                [--line-range line line]
                [files [files ...]]

Automatically formats Python code to conform to the PEP 8 style guide.

positional arguments:
  files                 files to format or '-' for standard in

optional arguments:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  -v, --verbose         print verbose messages; multiple -v result in more
                        verbose messages
  -d, --diff            print the diff for the fixed source
  -i, --in-place        make changes to files in place
  --global-config filename
                        path to a global pep8 config file; if this file does
                        not exist then this is ignored (default:
                        ~/.config/pep8)
  --ignore-local-config
                        don't look for and apply local config files; if not
                        passed, defaults are updated with any config files in
                        the project's root directory
  -r, --recursive       run recursively over directories; must be used with
                        --in-place or --diff
  -j n, --jobs n        number of parallel jobs; match CPU count if value is
                        less than 1
  -p n, --pep8-passes n
                        maximum number of additional pep8 passes (default:
                        infinite)
  -a, --aggressive      enable non-whitespace changes; multiple -a result in
                        more aggressive changes
  --experimental        enable experimental fixes
  --exclude globs       exclude file/directory names that match these comma-
                        separated globs
  --list-fixes          list codes for fixes; used by --ignore and --select
  --ignore errors       do not fix these errors/warnings (default: E24)
  --select errors       fix only these errors/warnings (e.g. E4,W)
  --max-line-length n   set maximum allowed line length (default: 79)
  --line-range line line, --range line line
                        only fix errors found within this inclusive range of
                        line numbers (e.g. 1 99); line numbers are indexed at
                        1

特性

autopep8会修复pep8汇报的下列问题：

E101 - Reindent all lines.
E121 - Fix indentation to be a multiple of four.
E122 - Add absent indentation for hanging indentation.
E123 - Align closing bracket to match opening bracket.
E124 - Align closing bracket to match visual indentation.
E125 - Indent to distinguish line from next logical line.
E126 - Fix over-indented hanging indentation.
E127 - Fix visual indentation.
E128 - Fix visual indentation.
E20  - Remove extraneous whitespace.
E211 - Remove extraneous whitespace.
E22  - Fix extraneous whitespace around keywords.
E224 - Remove extraneous whitespace around operator.
E226 - Fix missing whitespace around arithmetic operator.
E227 - Fix missing whitespace around bitwise/shift operator.
E228 - Fix missing whitespace around modulo operator.
E231 - Add missing whitespace.
E241 - Fix extraneous whitespace around keywords.
E242 - Remove extraneous whitespace around operator.
E251 - Remove whitespace around parameter '=' sign.
E26  - Fix spacing after comment hash for inline comments.
E265 - Fix spacing after comment hash for block comments.
E27  - Fix extraneous whitespace around keywords.
E301 - Add missing blank line.
E302 - Add missing 2 blank lines.
E303 - Remove extra blank lines.
E304 - Remove blank line following function decorator.
E309 - Add missing blank line (after class declaration).
E401 - Put imports on separate lines.
E501 - Try to make lines fit within --max-line-length characters.
E502 - Remove extraneous escape of newline.
E701 - Put colon-separated compound statement on separate lines.
E70  - Put semicolon-separated compound statement on separate lines.
E711 - Fix comparison with None.
E712 - Fix comparison with boolean.
E721 - Use "isinstance()" instead of comparing types directly.
W291 - Remove trailing whitespace.
W293 - Remove trailing whitespace on blank line.
W391 - Remove trailing blank lines.
W601 - Use "in" rather than "has_key()".
W602 - Fix deprecated form of raising exception.
W603 - Use "!=" instead of "<>"
W604 - Use "repr()" instead of backticks.
W690 - Fix various deprecated code (via lib2to3).

备注：

autopep8 也会忽略一些 pep8 的问题。

1. E112/E113

2. E265

autopep8 也会修复一个非pep8汇报的问题：

1. 纠正弃用的以及非惯用的python代码（通过 lib2to3）。这会让python 2.6 以及 python 2.7 的代码更加与 python3 兼容。（如果 W690 是enable的，这一项修复会被触发）

2. 标准化具有多种行结束符的文件。

3. 在类申明和它的第一个方法申明中间加一个空行。（由 E309 enable）

4. 在类文档和它的第一个方法申明中间加一个空行。（由 E301 enable）

5. 移除方法申明和它的文档之间的空行。 （由 E303 enable ）

具体用法

1. 使用 autopep8 更改一个文件。

假设文件名是 a.py，文件内容如下：

import math, sys;

def example1():
    ####This is a long comment. This should be wrapped to fit within 72 characters.
    some_tuple=(   1,2, 3,'a'  );
    some_variable={'long':'Long code lines should be wrapped within 79 characters.',
    'other':[math.pi, 100,200,300,9876543210,'This is a long string that goes on'],
    'more':{'inner':'This whole logical line should be wrapped.',some_tuple:[1,
    20,300,40000,500000000,60000000000000000]}}
    return (some_tuple, some_variable)
def example2(): return {'has_key() is deprecated':True}.has_key({'f':2}.has_key(''));
class Example3(   object ):
    def __init__    ( self, bar ):
     #Comments should have a space after the hash.
     if bar : bar+=1;  bar=bar* bar   ; return bar
     else:
                    some_string = """
                       Indentation in multiline strings should not be touched.
Only actual code should be reindented.
"""
                    return (sys.path, some_string)

转到 Python3Scripts 路径，可以看到 autopep8.exe 文件。

在a.py路径下，打开cmd，执行下列命令： 

D:Python3Scriptsautopep8 --in-place --aggressive --aggressive a.py

备注： 

--in-place： 以更改后的文件直接替代源文件。

--aggressive --aggressive : 以 aggressive 等级2 来更改源文件。

更改之后，a.py内容如下：

import math
import sys


def example1():
    # This is a long comment. This should be wrapped to fit within 72
    # characters.
    some_tuple = (1, 2, 3, 'a')
    some_variable = {
        'long': 'Long code lines should be wrapped within 79 characters.',
        'other': [
            math.pi,
            100,
            200,
            300,
            9876543210,
            'This is a long string that goes on'],
        'more': {
            'inner': 'This whole logical line should be wrapped.',
            some_tuple: [
                1,
                20,
                300,
                40000,
                500000000,
                60000000000000000]}}
    return (some_tuple, some_variable)


def example2(): return ('' in {'f': 2}) in {'has_key() is deprecated': True}


class Example3(object):

    def __init__(self, bar):
        # Comments should have a space after the hash.
        if bar:
            bar += 1
            bar = bar * bar
            return bar
        else:
            some_string = """
                       Indentation in multiline strings should not be touched.
Only actual code should be reindented.
"""
            return (sys.path, some_string)

2. aggressive 等级

默认情况下，autopep8只修复空格问题。所以，默认情况下，autopep8不会修复 E711 和 E712 ，也不会修复弃用的代码 W6。

为了应用这些更加 aggressive 的修复，使用 --aggressive 选项：

autopep8 --aggressive a.py

使用多个 --aggressive 可以增加 aggressiveness 等级。

比如， E712 需要 aggressiveness 等级2.

autopep8 --aggressive  --aggressive a.py

3. 选择修复部分规范

只修复一部分规范，使用 --select 选项。

比如，修复多种缩进问题：

$ autopep8 --select=E1,W1 a.py

仅仅修复弃用代码问题：

$ autopep8 --aggressive --select=W6 a.py

4. 显示详细的过程信息

$ autopep8 -v a.py

5. 以模块的方式使用

>>> import autopep8
>>> autopep8.fix_code('x=       123
')
'x = 123
'

 6. 以模块的方式使用，且带有条件

>>> import autopep8
>>> autopep8.fix_code('x.has_key(y)
', options={'aggressive': 1})
'y in x
'
>>> autopep8.fix_code('print( 123 )
', options={'ignore': ['E']})
'print( 123 )
'