正则表达式

cheatsheet

Python Regular Expression Quick Guide

• ^ Matches the beginning of a line $Matches the end of the line • . Matches any character • \s Matches whitespace • \S Matches any non­whitespace character • * Repeats a character zero or more times • *? Repeats a character zero or more times (non­greedy) • + Repeats a character one or more times • +? Repeats a character one or more times(non­greedy) • [aeiou] Matches a single character in the listed set • [^XYZ] Matches a single character not in the listed set • [a­-z0-­9] The set of characters can in clude arange • ( Indicates where string extraction is to start • ) Indicates where string extraction is to end re库里的文档 The special characters are: "." Matches any character except a newline. "^" Matches the start of the string. "$"      Matches the end of the string or just before the newline at
the end of the string.
"*"      Matches 0 or more (greedy) repetitions of the preceding RE.
Greedy means that it will match as many repetitions as possible.
"+"      Matches 1 or more (greedy) repetitions of the preceding RE.
"?"      Matches 0 or 1 (greedy) of the preceding RE.
*?,+?,?? Non-greedy versions of the previous three special characters.
{m,n}    Matches from m to n repetitions of the preceding RE.
{m,n}?   Non-greedy version of the above.
"\\"    Either escapes special characters or signals a special sequence.
[]       Indicates a set of characters.
A "^" as the first character indicates a complementing set.
"|"      A|B, creates an RE that will match either A or B.
(...)    Matches the RE inside the parentheses.
The contents can be retrieved or matched later in the string.
(?iLmsux) Set the I, L, M, S, U, or X flag for the RE (see below).
(?:...)  Non-grouping version of regular parentheses.
(?P<name>...) The substring matched by the group is accessible by name.
(?P=name)     Matches the text matched earlier by the group named name.
(?#...)  A comment; ignored.
(?=...)  Matches if ... matches next, but doesn't consume the string.
(?!...)  Matches if ... doesn't match next.
(?<=...) Matches if preceded by ... (must be fixed length).
(?<!...) Matches if not preceded by ... (must be fixed length).
(?(id/name)yes|no) Matches yes pattern if the group with id/name matched,
the (optional) no pattern otherwise.

The special sequences consist of "\\" and a character from the list
below.  If the ordinary character is not on the list, then the
resulting RE will match the second character.
\number  Matches the contents of the group of the same number.
\A       Matches only at the start of the string.
\Z       Matches only at the end of the string.
\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].
\s       Matches any whitespace character; equivalent to [ \t\n\r\f\v].
\S       Matches any non-whitespace character; equiv. to [^ \t\n\r\f\v].
\w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_].
With LOCALE, it will match the set [0-9_] plus characters defined
as letters for the current locale.
\W       Matches the complement of \w.
\\       Matches a literal backslash.

This module exports the following functions:
match    Match a regular expression pattern to the beginning of a string.
search   Search a string for the presence of a pattern.
sub      Substitute occurrences of a pattern found in a string.
subn     Same as sub, but also return the number of substitutions made.
split    Split a string by the occurrences of a pattern.
findall  Find all occurrences of a pattern in a string.
finditer Return an iterator yielding a match object for each match.
compile  Compile a pattern into a RegexObject.
purge    Clear the regular expression cache.
escape   Backslash all non-alphanumerics in a string.


练习1

import re
print = sum([int(x) for x in re.findall('[0-9]+',open('sample.txt').read())])


greedy

import re
x = 'From: Using the : character'
y = re.findall('^F.+:', x)
print y

['From: Using the :']

import re
x = 'From: Using the : character'
y = re.findall('^F.+?:', x)  # 加了个?
print y

['From:']


练习2

    \w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_].
With LOCALE, it will match the set [0-9_] plus characters defined
as letters for the current locale.
\W       Matches the complement of \w.


\w对应字母和数字，\W\w的补集

import re
re.sub('\W+', '', my_string)


n [1]: x = '#*cat36*:'

In [2]: import re

In [3]: re.sub('\W+', '', x)
Out[3]: 'cat36'


In [4]: "***foo ?! bar".translate(None, "*?!")
Out[4]: 'foo  bar'


练习3

header = "Host: www.google.com\nConnection: keep-alive\nAccept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5\nUser-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_6; en-US) AppleWebKit/534.13 (KHTML, like Gecko) Chrome/9.0.597.45 Safari/534.13\nAccept-Encoding: gzip,deflate,sdch\nAvail-Dictionary: GeNLY2f-\nAccept-Language: en-US,en;q=0.8\n"


import re
`