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。