Python PEP8 代码规范常见问题及解决方法

之前一直用 Python IDLE 写代码，最近换成 PyCharm 写代码总是会出现波浪号，这才了解到 Python 的 PEP8 代码规范，所以将常见的 PEP8 代码规范问题和解决方法记录一下，学习一下，遇到了再持续更新，养成良好的习惯，编写规范的代码！

PEP的全称是Python Enhancement Proposals，其中Enhancement是增强改进的意思，Proposals则可译为提案或建议书，所以合起来，比较常见的翻译是Python增强提案或Python改进建议书。

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• PEP 8: no newline at end of file
  解决方法：代码末尾需要另起一行，光标移到最后回车即可

• PEP 8: indentation is not a multiple of four
  解决方法：缩进不是4的倍数，检查缩进

• PEP 8: over-indented
  解决方法：过度缩进，检查缩进

• PEP 8: missing whitespace after’,’
  解决方法：逗号后面少了空格，添加空格即可，类似还有分号或者冒号后面少了空格

• PEP 8: multiple imports on one line
  解决方法：不要在一句 import 中引用多个库，举例：import socket, urllib.error最好写成：import socket import urllib.error

• PEP 8: blank line at end of line
  解决方法：代码末尾行多了空格，删除空格即可

• PEP 8: at least two spaces before inline comment
  解决方法：代码与注释之间至少要有两个空格

• PEP 8: block comment should start with ‘#’
  解决方法：注释要以#加一个空格开始

• PEP 8: inline comment should start with ‘#’
  解决方法：注释要以#加一个空格开始

• PEP 8: module level import not at top of file
  解决方法：import不在文件的最上面，可能之前还有其它代码

• PEP 8: expected 2 blank lines，found 0
  解决方法：需要两条空白行，添加两个空白行即可

• PEP 8: function name should be lowercase
  解决方法：函数名改成小写即可

• PEP 8: missing whitespace around operator
  解决方法：操作符（’=’、’>’、’<'等）前后缺少空格，加上即可

• PEP 8: unexpected spaces around keyword / parameter equals
  解决方法：关键字/参数等号周围出现意外空格，去掉空格即可

• PEP 8: multiple statements on one line (colon)
  解决方法：多行语句写到一行了，比如：if x == 2: print('OK')要分成两行写

• PEP 8: line too long (82 > 79 characters)
  解决方法：超过了每行的最大长度限制79

• PEP 8: Simplify chained comparison
  可简化连锁比较（例如：if a >= 0 and a <= 9: 可以简写为：if 0 <= a <= 9:）

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如果想要选择性忽略PEP8代码风格的警告信息可以使用以下方法：（养成良好的习惯，编写规范的代码！不推荐忽略！）

①将鼠标移到出现警告信息的地方，按 alt+Enter，选择忽略（Ignore）这个错误即可：

②依次选择 File - Settings - Editor - Inspections，在 Python下找到 PEP8 coding style violation 选项，在右下角的 Ignore errors 里点击加号可以添加需要忽略的警告信息ID（ID信息见后面附录），例如想要忽略indentation contains mixed spaces and tabs这个警告，只需要添加其ID：E101 即可

附录：全部警告信息以及对应的ID，官方地址：https://pep8.readthedocs.io/en/latest/intro.html#error-codes

code	sample message
E1	Indentation
E101	indentation contains mixed spaces and tabs
E111	indentation is not a multiple of four
E112	expected an indented block
E113	unexpected indentation
E114	indentation is not a multiple of four (comment)
E115	expected an indented block (comment)
E116	unexpected indentation (comment)
E117	over-indented
E121 (*^)	continuation line under-indented for hanging indent
E122 (^)	continuation line missing indentation or outdented
E123 (*)	closing bracket does not match indentation of opening bracket’s line
E124 (^)	closing bracket does not match visual indentation
E125 (^)	continuation line with same indent as next logical line
E126 (*^)	continuation line over-indented for hanging indent
E127 (^)	continuation line over-indented for visual indent
E128 (^)	continuation line under-indented for visual indent
E129 (^)	visually indented line with same indent as next logical line
E131 (^)	continuation line unaligned for hanging indent
E133 (*)	closing bracket is missing indentation
E2	Whitespace
E201	whitespace after ‘(‘
E202	whitespace before ‘)’
E203	whitespace before ‘:’
E211	whitespace before ‘(‘
E221	multiple spaces before operator
E222	multiple spaces after operator
E223	tab before operator
E224	tab after operator
E225	missing whitespace around operator
E226 (*)	missing whitespace around arithmetic operator
E227	missing whitespace around bitwise or shift operator
E228	missing whitespace around modulo operator
E231	missing whitespace after ‘,’, ‘;’, or ‘:’
E241 (*)	multiple spaces after ‘,’
E242 (*)	tab after ‘,’
E251	unexpected spaces around keyword / parameter equals
E261	at least two spaces before inline comment
E262	inline comment should start with ‘# ‘
E265	block comment should start with ‘# ‘
E266	too many leading ‘#’ for block comment
E271	multiple spaces after keyword
E272	multiple spaces before keyword
E273	tab after keyword
E274	tab before keyword
E275	missing whitespace after keyword
E3	Blank line
E301	expected 1 blank line, found 0
E302	expected 2 blank lines, found 0
E303	too many blank lines (3)
E304	blank lines found after function decorator
E305	expected 2 blank lines after end of function or class
E306	expected 1 blank line before a nested definition
E4	Import
E401	multiple imports on one line
E402	module level import not at top of file
E5	Line length
E501 (^)	line too long (82 > 79 characters)
E502	the backslash is redundant between brackets
E7	Statement
E701	multiple statements on one line (colon)
E702	multiple statements on one line (semicolon)
E703	statement ends with a semicolon
E704 (*)	multiple statements on one line (def)
E711 (^)	comparison to None should be ‘if cond is None:’
E712 (^)	comparison to True should be ‘if cond is True:’ or ‘if cond:’
E713	test for membership should be ‘not in’
E714	test for object identity should be ‘is not’
E721 (^)	do not compare types, use ‘isinstance()’
E722	do not use bare except, specify exception instead
E731	do not assign a lambda expression, use a def
E741	do not use variables named ‘l’, ‘O’, or ‘I’
E742	do not define classes named ‘l’, ‘O’, or ‘I’
E743	do not define functions named ‘l’, ‘O’, or ‘I’
E9	Runtime
E901	SyntaxError or IndentationError
E902	IOError
W1	Indentation warning
W191	indentation contains tabs
W2	Whitespace warning
W291	trailing whitespace
W292	no newline at end of file
W293	blank line contains whitespace
W3	Blank line warning
W391	blank line at end of file
W5	Line break warning
W503 (*)	line break before binary operator
W504 (*)	line break after binary operator
W505 (*^)	doc line too long (82 > 79 characters)
W6	Deprecation warning
W601	.has_key() is deprecated, use ‘in’
W602	deprecated form of raising exception
W603	‘<>’ is deprecated, use ‘!=’
W604	backticks are deprecated, use ‘repr()’
W605	invalid escape sequence ‘x’
W606	‘async’ and ‘await’ are reserved keywords starting with Python 3.7