\d+)\.(\d*)'. For the remainder of this section, all regular expression patterns are denoted using the raw string syntax. The following special- character sequences are recognised in regular expression patterns: text matches the literal string text . matches any character except new line ^ matches start of the string $ matches the end of the string * matches zero or more repetitions of preceding element + matches one or more repetitions of the preceding element ? matches zero repetitions or one repetition of preceding expression *? matches zero or more preceding elements, as few as possible +? matches one or more preceding elements, as few as possible ?? matches zero or one preceding element as few as possible {m} matches exactly m repetitions of the preceding element {m, n} matches m to n repetitions of the preceding expression, matching as many as possible {m, n}? matches m to n repetitions of the preceding expression, matching as few as possible [. . .] matches a set of characters such as r'[abcdef]', special characters are not active inside this set. [^. . .] matches characters that are not defined in the set a|b matches a or b, where a and b both are regular expressions (?: . . .) matches the regular expression in the string but discards the matched substring. (?#. . . ) A comment. Content inside the parentheses is ignored. (?! . . .) matches the preceding expression only if it's not followed by the pattern in parentheses. (?

Regular expressions in Python

05 min read

A regular expression pattern is a sequence of characters that will match sequences of characters in a target. These can be accessed in Python by importing the module "re". The "re" module is used to perform regular-expression pattern matching and replacement in strings. Both ordinary and Unicode strings are supported. Regular expression patterns are specified as strings containing a mix of text and special- character sequences. Because patterns often make extensive use of special characters and the backlash, they are usually written as "raw" strings, such as r' (?P<int>\d+)\.(\d*)'. For the remainder of this section, all regular expression patterns are denoted using the raw string syntax.

The following special- character sequences are recognised in regular expression patterns:

text                   matches the literal string text

.                          matches any character except new line

^                         matches start of the string

$                        matches the end of the string

*                         matches zero or more repetitions of preceding element

+                        matches one or more repetitions of the preceding element

?                         matches zero repetitions or one repetition of preceding expression

*?                       matches zero or more preceding elements, as few as possible

+?                      matches one or more preceding elements, as few as possible 

??                      matches zero or one preceding element as few as possible 

{m}                  matches exactly m repetitions of the preceding element 

{m, n}             matches m to n repetitions of the preceding expression, matching as many as possible 

{m, n}?          matches m to n repetitions of the preceding expression, matching as few as possible

[. . .]               matches a set of characters such as r'[abcdef]', special characters are not active inside this set.

[^. . .]            matches characters that are not defined in the set

a|b               matches a or b, where a and b both are regular expressions

(?: . . .)         matches the regular expression in the string but discards the matched substring.

(?#. . . )         A comment. Content inside the parentheses is ignored.

(?! . . .)           matches the preceding expression only if it's not followed by the pattern in parentheses.

(?<! . . .)         matches the following expression only if it's not preceded by a match of the pattern in the parantheses.

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