[Python] - Regular expression

Regular Expression

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1.meta characters

. ^ $ * + ? { } [ ] \ | ( )

1.1) character class []

• regular expression between [ and ] is matching characters
• '-' operator mean From - To ( [0-5] -> [012345] )
• '^' operator mean Not
• '.' operator mean all characters except \n
• '*' operator mean repeat characters 0~N ( N maybe 2000000000 because memory limit )
• '+' operator mean repeat characters 1~N 
• {m,n} operator mean repeat characters M~N
• '?' operator mean repeat characters 0~1

#regular expression
[abc]

# match
a
# match
before
# not match
dededede

# alphabet
[a-zA-Z]
# number
[0-9] = \d
# Not number
[^0-9] = \D

# Match whitespace characters
[ \t\n\r\f\v] = \s
# Not Match whitespace characters
[^ \t\n\r\f\v] = \S

# Match number+alpha 
[a-zA-Z0-9_] = \w
# Not Match number+alpha 
[a-zA-Z0-9_] = \W

# a+all characters+b
[a.b]
# Match a.b
[a[.]b]

 

2. Python regular expression

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syntax

import re
p = re.compile('[a-z]+')

1. Match function

• match string data and regular expression

import re
p = re.compile('[a-z]+')

target = "python"
m = p.match(target)
# re.match('[a-z]+' , "python")

if m :
	print('match {}'.format(m.group())

target = "1234"
# None
m = p.match(target)
if m :
	print('not match')

2. Search function

• matach all string data and regular expression

import re
p = re.compile('[a-z]+')
m = p.search('1234 Python')
# re.search('[a-z]+' , "1234 Python")

if m :
	print(m.group())
> ython

3. Findall function

• return list string data match regular expression

import re
p = re.compile('[0-9]+')
result = p.findall("life0s.12tooshort")
# re.findall('[0-9]+',"life0s.12tooshort")

print(result)
> ['0', '12']

 

4. Match method

• Object Match has group() , start() , end() , span() function
• group() is return match characters
• start() is return match characters start index
• end() is return match characters end index
• span() is return match characters (start,end) index

>>> m = p.match("python")
>>> m.group()
'python'
>>> m.start()
0
>>> m.end()
6
>>> m.span()
(0, 6)