python的正则表达式

Posted 2021-05-02 编程坑太多

比较多用于过滤条件，先确认想要过滤的信息，确认此信息和其他信息的不同。（找出特点）
然后对着正则表达式的列表转码就行。
基本其他的编程语言都有，linux一般常见于grep处理文本。

python的库几乎都不用记，想查可以import x, dir(x)来看

#for linux
$ grep '^From:' mbox-short.txt

记录一些python re常见的符号和用法，来自py4e

^ Matches the beginning of the line.
$ Matches the end of the line.
. Matches any character (a wildcard).
\s Matches a whitespace character.
\S Matches a non-whitespace character (opposite of \s).
* Applies to the immediately preceding character and indicates to match zero or more of the preceding character(s).
*? Applies to the immediately preceding character and indicates to match zero or more of the preceding character(s) in "non-greedy mode".
+ Applies to the immediately preceding character and indicates to match one or more of the preceding character(s).
+? Applies to the immediately preceding character and indicates to match one or more of the preceding character(s) in "non-greedy mode".
[aeiou] Matches a single character as long as that character is in the specified set. In this example, it would match "a", "e", "i", "o", or "u", but no other characters.
[a-z0-9] You can specify ranges of characters using the minus sign. This example is a single character that must be a lowercase letter or a digit.
[^A-Za-z] When the first character in the set notation is a caret, it inverts the logic. This example matches a single character that is anything other than an uppercase or lowercase letter.
( ) When parentheses are added to a regular expression, they are ignored for the purpose of matching, but allow you to extract a particular subset of the matched string rather than the whole string when using findall().
\b Matches the empty string, but only at the start or end of a word.
\B Matches the empty string, but not at the start or end of a word.
\d Matches any decimal digit; equivalent to the set [0-9].
\D Matches any non-digit character; equivalent to the set [^0-9].
greedy matching
The notion that the "+" and "*" characters in a regular expression expand outward to match the largest possible string.

用dir查询库里含有的模块

>>> import re
>>> dir(re)
[.. 'compile', 'copy_reg', 'error', 'escape', 'findall',
'finditer', 'match', 'purge', 'search', 'split', 'sre_compile',
'sre_parse', 'sub', 'subn', 'sys', 'template']
>>> help (re.search)
Help on function search in module re:

MATCH1.png

MATCH2.png

查找全部内容

re.findall

greedy matching 外扩到能找的最多为止。

greedy-matching.png

non-greedy matching ,找到最短契合的。