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Python regular expression is an expression that briefly expresses a set of strings. Regular expressions can easily check whether a string matches a certain pattern. There are six common functions in regular expressions: re.match, re.search, re.findall, re.compile, re.split, and re.sub.

The re.match () tch function matches from scratch, and if the starting position match is not successful, the matching result of the match function is none.

Re.search () the entire string and returns the first successful match

Re.findall () the entire string that returns a list (the most commonly used)

The re.compile () # compile function is used to compile a regular expression to generate a regular expression (Pattern) object

Re.split () # splits a string according to the result of regular expression matching and returns the list type

Re.sub () # replaces all the substrings that match the regular expression in a string and returns the replaced string

1. Re.match function

The match function matches from scratch, and if the starting position match is not successful, the matching result of the match function is none. If the match succeeds, the re.match method returns a matching object.

The syntax is as follows: re.match (pattern, string, flags=0)

Pattern: regular expressions that need to be matched

String: just match in that string

Flags: flag bit (default is 0), which controls how regular expressions are matched

Common flags is as follows:

Re.I ignores case when matching

Re.M multiline matching, affecting ^ and $

Re.S. The default does not match line breaks, so that. Match all characters, including line breaks

Re.U parses characters based on the Unicode character set. This flag affects\ w,\ W,\ b,\ B

Examples are as follows:

We can see that if the match function matches successfully, the re.match method returns a matching object instead of a matching regular expression; the matching position can be obtained through span ().

> import re

> astr='11you are 3344 my apple\ n11 pistachios, you\ n66a77'

> re.match

> re.match ('11 years journal astr). Span ()

(0,2)

> print (re.match ('you',astr))

None

2. Re.search function

Searches the entire string and returns the first successful match.

The syntax is as follows: re.search (pattern, string, flags=0)

Pattern: regular expressions that need to be matched

String: just match in that string

Flags: flag bit (default is 0), which controls how regular expressions are matched

Common flags is as follows:

Re.I ignores case when matching

Re.M multiline matching, affecting ^ and $

Re.S. The default does not match line breaks, so that. Match all characters, including line breaks

Re.U parses characters based on the Unicode character set. This flag affects\ w,\ W,\ b,\ B

Examples are as follows:

We can see that if the search function matches successfully, the re.search method returns a matching object instead of a matching regular expression; the matching position can be obtained through span (). If there is no match, it is returned as None.

> import re

> astr='11you are 3344 my apple\ n11 pistachios, you\ n66a77'

> re.search

> re.search ('you',astr)

> re.search ('you',astr). Span () # get the matching position through span ()

(2, 5)

> re.search ('11 years journal astr). Span ()

(0,2)

> print (re.search ('22 million dint ASTM))

None

3. Re.findall function

Search the entire string and return a list

Syntax is as follows: re.findall (string)

> import re

> astr='1you are 3344 my apple\ n11 pistachios, you\ n66a77'

>

['33,'44,'11,'66,'77]

> re.findall ('\ d {2Magne4}', astr) # list shows all the four numbers of 2muri, which matches greedily by default.

['3344,' 11,'66,'77]

> re.findall ('\ dflowers, last minute ASTM) # (1, infinity)

['1', '3344','11','66','77']

> re.findall ('\ dflowers, no matter how much) # (0, infinity)

['1', '3344,' 11,'66,'' '77 years,']

> re.findall ('\ dflowers match 1 / 0) # match 0 or 1

['1mm,' 3mm, '3mm,' 4pm, '4pm,' 1mm, '1mm,'' ',' 6percent, '6percent,', '7percent,' 7percent,'']

> re.findall ('\ d {2jue 3}?, astr) # A pattern followed by? Oh, not greedy matching, behind the range? Twice, just take it twice first.

['33,'44,'11,'66,'77]

>

['334', '6a7']

> re.findall ('^\ dharmjime) # begins with a number

['1']

> re.findall ('^\ dBell _ pr _ astro _ re.M) # multiline matching

['1mm,' 6']

> re.findall ('\ dflowers, girls, etc.) # ends with a number

['7']

> re.findall ('\ daddy match, which affects ^ and $

['7']

> re.findall ('\ d (.) (\ d)', astr,re.S) # is returned as a list, and each item is a tuple

[('3percent,' 4'), ('averse,' 7')]

4. Re.compile function

The compile function is used to compile a regular expression to generate a regular expression (Pattern) object.

Syntax is as follows: re.compile (pattern,flags=0)

Pattern: regular expressions that need to be matched

Flags: flag bit (default is 0), which controls how regular expressions are matched

Common flags is as follows:

Re.I ignores case when matching

Re.M multiline matching, affecting ^ and $

Re.S. The default does not match line breaks, so that. Match all characters, including line breaks

Re.U parses characters based on the Unicode character set. This flag affects\ w,\ W,\ b,\ B

Examples are as follows:

> import re

> astr='AS12as34er567q! "3456'

> m1=re.compile (r'\ d\ d') # compile

> m1.search (astr). Group () # match

'12'

> m1.findall (astr)

['12,'34,'56,'34,'56]

>

> > m2.findall (astr) # match

['Abigail,' a']

5. Re.split function

Splits a string according to the result of a regular expression match and returns the list type.

Syntax is as follows: re.split (pattern, string,? maxsplit=0?,flags=0)

Pattern: regular expressions that need to be matched

String: just match in that string

Maxsplit: number of separations. Maxsplit=1 separates once. Default is 0. There is no limit on the number of separations.

Flags: flag bit (default is 0), which controls how regular expressions are matched.

Common flags is as follows:

Re.I ignores case when matching

Re.M multiline matching, affecting ^ and $

Re.S. The default does not match line breaks, so that. Match all characters, including line breaks

Re.U parses characters based on the Unicode character set. This flag affects\ w,\ W,\ b,\ B

Examples are as follows:

> import re

> astr='AS12as34er567q! "3456'

> astr.split ('12') # split by 12

['AS',' as34er567q! "3456']

> re.split ("\ d {2}", astr) # split by two numbers

['AS',' as', 'er',' 7q! ",',']

> re.split ("\ d +", astr) # split by numbers

['AS',' as', 'er',' Q! ",']

>

> m3.split (astr)

['AS',' as', 'er',' Q! ",']

> m3.split (astr,3) # specify how many times to split

['AS',' as', 'er',' Q! "3456']

6. Re.sub function

Replaces all substrings that match the regular expression in a string and returns the replaced string.

The syntax is as follows: re.sub (pattern, repl, string, count=0,flags=0)

Pattern: regular expressions that need to be matched

Repl: the replacement string, which can also be a function.

String: just match in that string

Count: the maximum number of substitutions after a pattern match. The default of 0 means replacing all matches.

Flags: flag bit (default is 0), which controls how regular expressions are matched

Common flags is as follows:

Re.I ignores case when matching

Re.M multiline matching, affecting ^ and $

Re.S. The default does not match line breaks, so that. Match all characters, including line breaks

Re.U parses characters based on the Unicode character set. This flag affects\ w,\ W,\ b,\ B

Examples are as follows:

> import re

> astr='AS12as34er567q! "3456'

> re.sub ("5", '9century centr) # replace 5 with 9

'AS12as34er967q!' 3496'

> m4=re.compile (r "\ d +")

> m4.sub ('', astr) # replace the number with an empty string

'AS as er q!'

> m4.sub ('', astr,2) # specifies how many times to replace

'AS as er567q! '3456

That's all of the article "there are several functions for Python regular expressions". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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