Python Regular Expression

Regular expression in Python

^	Matches the beginning of a line
$	Matches the end of the line
.	Matches any character
\s	matches whitespace
\S	matches any non-whitespace
*	repeats a character 0 or more times
*?	repeats a character 0 or more times(non-greedy)
+	repeats a character 1 or more times
+?	repeats a character 1 or more times(non-greedy)
[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 include a range
(	indicates where string extraction is to start
)	indicates where string extraction is to end

Greedy Matching

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

Output:

['From: Using the :']

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

Output:

['From: Using the :']

NON-Greedy Matching

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

Output:

['From:']

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

Output:

['From:']

说明：在字符串'From:Using the :character' 中， 有两个: 号存在。 当要匹配以F开头，以: 号结尾的字符串时，GreedyMatching 会以Greedy 为原则找到尽可能长的匹配字符串。 而NON-Greedy Matching 不会像Greedy 那样去找尽可能长的串。