How to match string with python regular expression?

#How to match strings with python regular expressions?

How to match strings with python regular expressions:

1. String matching at a single position

In this case we You can use this (. ?) regular expression to extract. For example, a string "a123b", if we want to extract the value 123 between ab, we can use findall with the regular expression, which will return a string that matches the situation list, 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 all values ​​between a and the last b instead of The value 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 To match multiple lines, you need to add the re.S and re.M flags. After adding re.S, . will match newlines. By default, newlines will not be matched. 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')]

Add After re.M is added, 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. Match strings in multiple consecutive positions

In this case we can use the regular expression (?P...) to extract. For example, if we have a line of webserver 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 content in this log line, we can write multiple (?Pexpr) To extract, name can be changed to the variable you named the string at that location, and expr can be changed to the regular expression of the extraction location. 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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