Regular expression

   Regular expressions themselves are small 、 Highly specialized programming language , And in the python in , Through embedded Integration re modular , Can be called directly to achieve regular matching , Retrieve and replace those that match a pattern ( The rules ) Text, etc .

   The following describes common functions and their parameters , Modifier , And the usage of various pattern rules .

compile(pattern, flags=0)

For compiling regular expressions , Generate a regular expression （ Pattern ） Object supply match() and search() And so on .

Match at least one number from the beginning of the string , return None

From specified Index 9,13 Start matching at the string position of , return None

From specified Index 10,13 Start matching at the string position of , return 12, The match is successful

return Index Starting position

return Index End position

return Index Range

Another one compile Function example ： Add modifier re.I and group() Method directly outputs the matching string

group(1) and group(2) The output results are grouping 1, 2 Result

groups() Method , Direct output contains grouping 1 And grouping 2 Of tuple

amount to result.groups() = (result.group(1), result.group(2)…)

therefore group(1) & group(2) It can also be done through tuple Method of value taking , Direct output

match(pattern, string, flags=0)

from string Start at the beginning of the string Match target object pattern, If the match is successful , Return match object ; If no match is found , Then for “None”

fullmatch(pattern, string, flags=0)

Try the regular expression pattern Apply to all strings string, If 100% The match is successful , Return match object ; If no match is found , Then for “None”

search(pattern, string, flags=0)

Scan string string To find a regular expression pattern Matches for , Return match object ; If no match is found , Then for “None”

split(pattern, string, maxsplit=0, flags=0)

By regular expression pattern The rules of Division maxsplit Substring , And return to the list

With “b* " by pattern object , Because the string has no letters b, Add *b pattern amount to ’ '( Blank content ） No matching letters b, Split each character of the string

hold * Get rid of , It is equivalent to not matching the corresponding character , No segmentation , Finally, output the list of original strings

add to maxsplit by 1 when , Output contain 2 A string A list of

With ’ \W+’ by pattern, matching 1 One or more non alphanumeric characters and underscores , Split the string into 4 A list of strings , The last character is null

With (’ \W+’ ) by pattern, String in the output list , The symbol contained in the original string is an independent character in the list

The same to (’ \W+’ ) by pattern, Add a space at the beginning of the original string
Number in the output list 2 A string , For a space

With ’ \W+’ by pattern, add to maxsplit by 1 when , Output contain 2 A string A list of

With ‘r\s+’ by pattern, matching 1 One or more arbitrary white space characters , Split into 4 A list of characters

amount to Direct string splitting method ： str.split()

findall(pattern, string, flags=0)

In string string Match all regular expressions in pattern The object of , And pass these objects through the list list Form return of

With r’\W+’ by pattern, matching 1 One or more non alphanumeric characters and underscores , Output, respectively, 2 A list ,1 Yes Space and ！ A list of independent characters ; The other is Only Space A list of , By adding Index Range

sub(pattern, repl, string, count=0, flags=0)

Use regular expressions pattern To match the original string string, And replace the matched content with repl, It can be used count Specify the number of replacements

repl : Replaced string , It can also be a function
string : The original string to be found and replaced
count : The maximum number of substitutions after pattern matching , Default 0 Means to replace all matches

With r’\D’ by pattern, Match any non number , Put the number of ’-‘ Get rid of

With r’#.*$’ by pattern, Match any character （ except \n Outside ）, Put the back of the phone Remove comments from

subn(pattern, repl, string, count=0, flags=0)

Use regular expressions pattern To match the original string string, And replace the matched content with repl And return the quantity replaced

With r’\D’ by pattern, Match any non number , Put the number of ’-‘ Get rid of , The final result is a tuple, Contains the matching results And the number of matches

finditer(pattern, string, flags=0)

In string string Match all regular expressions in pattern The object of , And return these objects in the form of iterators

With r’\d+’ by pattern, matching 1 One or more numbers , hold 12, 32, 43 and 3 Save to iterator , Through the loop , Output 4 Group numbers

escape(pattern)

Escape a special character in a string , That is to add... Before each special character \

re.I (re.IGNORECASE)

Make match match case insensitive

re.M (re.MULTILINE)

Multi-line matching , Multi line mode , When there is a line break in a string \n, Line breaks are not supported in default mode , such as ： The beginning of the line and End of line , In multiline mode, matching line start is supported

re.S (re.Dotall)

DOT Express .,ALL Express all , All in all . Match all , Include line breaks \n

In default match mode . There is no match for newline \n, Instead, match strings separately ; And in the re.DOTALL In mode , A newline \n Match with string to .

re.X (re.VERBOSE)

Detailed mode , You can annotate regular expressions

{n}

matching n Time

With r’\d{8}’ by pattern, Before matching 8 Digit number

{n,}

Match at least n Time

With r’\d{10,}’ by pattern, Strings share 11 position , The matching result is 11 digit , Conform to the rules

When it comes to {12,} , because n < len(str) , So there's an error

{n,m}

Match at least n Times and no more than m Time (n<=m)

With r’\d{9,10}’ by pattern, The result is The complete string is 10 Digit number

If replaced {10,9 } because n < m, Not in line with the rules , Will report a mistake

If { 9,13}, although 13 Beyond the len(str) , But it can also be matched successfully , It is equivalent to that the slice is out of range , No errors reported .

\b

Matches a word boundary , for example , ‘er\b’ Can match ‘worker’ Medium ‘er’, But can't match ‘every’ Medium ‘er’

\B

Match non word boundaries .‘er\B’ Can match ‘every’ Medium ‘er’, But can't match ‘worker’ Medium ‘er’