How to match string with python regular expression

How to match strings with python regular expressions: 1. Use the regular expression [(. ?)] to extract the string at a single position; 2. Use [(?P…)] This regular expression [matches strings in multiple consecutive positions.

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Python regular expression method of matching strings:

1. String extraction at a single position

In this case we can use the regular expression

(. ?) to extract. For example, for a string "a123b", if we want to extract the value 123 between ab, we can use findall with a regular expression, which will return a list containing all the conditions that match the situation.

The code is as follows:

import re
str = "a123b"
print re.findall(r"a(.+?)b",str)#
输出['123']

1.1 Greedy and non-greedy matching

If we have a string "a123b456b", if we want to match a and All values ​​between the last b instead of the values ​​between a and the first occurrence of b can be used to control regular greedy and non-greedy matching.

The code is as follows:

import re
str = "a123b456b"
 
print re.findall(r"a(.+?)b", str)
#输出['123']#?控制只匹配0或1个,所以只会输出和最近的b之间的匹配情况
 
print re.findall(r"a(.+)b", str)
#输出['123b456']
 
print re.findall(r"a(.*)b", str)
#输出['123b456']

1.2 Multi-line matching

If you want multi-line matching, you need to add re.S and re.M Logo. After adding re.S. Will match newline characters, default. Will not match newline characters.

The code is as follows:

str = "a23b\na34b"
 
re.findall(r"a(\d+)b.+a(\d+)b", str)
#输出[]
#因为不能处理str中间有\n换行的情况
 
re.findall(r"a(\d+)b.+a(\d+)b", str, re.S)
#s输出[('23', '34')]

After adding re.M, the ^$ mark will match each line. By default, ^ and $ will only match the first line.

The code is as follows:

str = "a23b\na34b"
 
re.findall(r"^a(\d+)b", str)
#输出['23']
 
re.findall(r"^a(\d+)b", str, re.M)
#输出['23', '34']

2. Extract strings at multiple consecutive positions

In this case we can use

(?P< ;name>…)This regular expression is used to extract. For example, if we have a line of webserver's access log:'192.168.0.1 25/Oct/2012:14:46:34 "GET /api HTTP/1.1" 200 44 "http://abc.com/search" "Mozilla/5.0"', we want to extract all the contents in this line of log, you can write multiple (?Pexpr) to extract, where the name can be changed to what you are For variables named by position strings, expr can be changed to the regular expression for extracting the position.

The code is as follows:

import re
line ='192.168.0.1 25/Oct/2012:14:46:34 "GET /api HTTP/1.1" 200 44 "http://abc.com/search"
"Mozilla/5.0"'
reg = re.compile(&#39;^(?P<remote_ip>[^ ]*) (?P<date>[^ ]*) "(?P<request>[^"]*)" 
(?P<status>[^ ]*) (?P<size>[^ ]*) "(?P<referrer>[^"]*)" "(?P<user_agent>[^"]*)"&#39;)
regMatch = reg.match(line)
linebits = regMatch.groupdict()
print linebits
for k, v in linebits.items() :
 print k+": "+v

The output result is:

status: 200
referrer: 
request: GET /api HTTP/1.1
user_agent: Mozilla/5.0
date: 25/Oct/2012:14:46:34size: 44
remote_ip: 192.168.0.1

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