Python Regular Expressions

1. Find the pattern in text: Re.search ()

Import"you ispython"= Re.search ('is'  , text)#  Returns the position of the first character of ' is ' in text, note that it is starting from 0 print(Match.start ())  #  Returns the position of the last character of ' is ' in text, which is starting from 1 print(Match.end ())

Results:

47

2. Compile expression: Compile ()

ImportRetext="You are SB"
# The Compile () function converts an expression string into a regexobject
Regexes={re.compile (P) forPinch['SB','NB','MB']           } forRegexinchregexes:ifRegex.search (text):Print('seeking'+ Regex.pattern +'>> Match')    Else:        Print('seeking'+ Regex.pattern +'>> not match')

Results:

not >> not match

3. Multiple matches: FindAll (), Finditer ()

The FindAll () function returns all strings that match the pattern and do not overlap.

Import"ab aa ab bb ab ba"
# Match all of the ' ab ' combinations of text to print(Re.findall ('ab', text))

Results:

[' ab ' ab ' ab ' ]

Finditer () returns an iterator

Import"ab aa ab bb ab ba" for in Re.finditer ('  AB', text):    = match.start ()    = match.end ()      Print('found {} at {} to {}'. Format ('"ab', STR (s), str (e)))

Results:

" AB  " at 0 to 2"ab "@ 6 to 8"ab "at 14

4. Pattern syntax

ImportRedefTest_patterns (Text,patterns = []):    #The pattern returns the first element of the patterns item, and DESC returns the second element of the patterns item, respectively.    #This function is equivalent to patterns the first item as a match condition to match the text     forPattern,descinchPatterns:Print('Matching method:'+ Pattern,'Description:'+desc)Print('Text:'+text) forMatchinchRe.finditer (pattern,text): s=Match.start () e=match.end ()Print('found {} at {} to {}, result:{}'. Format (Pattern,str (s), str (e), (text[s:e)))

Execute the function:

# matches all A, followed by 1 B.
>>> test_patterns (' ', [('ab','A Followed by B')])
2 to 45 to 79 to one, Result:ab>>>

Repeat

There are 5 methods in the pattern that represent repetition, and now one by one show:

#* indicates that the pattern repeats 0 or more times (repeating 0 times means that it does not appear and can be matched)#matches a start, followed by 0 or more B, that is, as long as a can match>>> Test_patterns ('a AC ab ABB ABBB',[('ab*','a followed by zero or more B')]) matching method: AB* Description: A followed by zeroorMore B text: A AC ab ABB ABBB found AB* At 0 to 1, Result:afound AB* At 2 to 3, Result:afound AB* At 5 to 7, Result:abfound AB* at 8 to 11, Result:abbfound AB* at 16, RESULT:ABBB>>>

 #   + indicates that the pattern appears at least once  #   
 >>> test_patterns ( '    

#The representation pattern appears 0 or 1 times#matches a start, followed by 0 or 1 B, that is, as long as a can match>>> Test_patterns ('a ab ABB abbb',[('ab+','a followed by one or more B')]) matching method: AB+ Description: A followed by oneorMore B text: A AB ABB ABBB found AB+ at 2 to 4, Result:abfound AB+ at 5 to 8, Result:abbfound AB+ at 9 to 13, RESULT:ABBB>>>

# match a start, followed by 3 b>>> test_patterns (', ['ab{3}' ,'a followed by three B')])
Matching method: ab{3} Description: A followed by three B text: A ab ABB abbb found ab{3} at 9 to, result:abbb>> ;>

# match a start, followed by 2 or 3 b>>> test_patterns ('', [('ab{2,3} 'A followed by or three B')]) match: ab{or  three B Text: A ab ABB abbb found ab{2,3} at 5 to 8, Result:abbfound ab{2,3} at 9 to, result:abbb> >>

Character

A character set is a set of characters that contain all the characters that can match the corresponding position in the pattern, such as [AB] to match A or b.

# match all A or B>>> test_patterns ('abca', [('[ab]' ,'either a or b'or11 to 23 to 4, result:a>>>

# match A to the beginning, followed by a or B >>> test_patterns ('a aa ab ac', [('A[ab]  ','a followed by a or B'or2 to 4  5 to 7, Result:ab>>>

# match a start, followed by 1 or more A or B >>> test_patterns ('a aaaaa abbb ACCC', [(' a[ab]+ 'A followed by 1 or more A or B')])) matches by: A[ab]oror
     B Text: A AAAAA abbb acccfound A[ab]+ at 2 to 7, Result:aaaaafound A[ab]+at 8 to, result:a BBB>>>

Python Regular Expressions