[Python Study Notes] Regular expressions

                     Regular Expressions                                                                   

A regular expression is a special sequence of characters that can help you easily check whether a string matches a pattern.

Python has added the RE module since version 1.5, which provides a Perl-style regular expression pattern.

The RE module enables the Python language to have all the regular expression functionality.

The compile function generates a regular expression object based on a pattern string and an optional flag parameter. The object has a series of methods for regular expression matching and substitution.

The RE module also provides functions that are fully consistent with these methods, which use a pattern string as their first parameter.

This section focuses on the regular expression handlers commonly used in Python.

Re.match function

Re.match attempts to match a pattern from the starting position of the string, and if the match is not successful, match () returns none.

function Syntax :

string, flags=0)

Parameters	Description
Pattern	Matched regular Expressions
String	The string to match.
Flags	A flag bit that controls how regular expressions are matched, such as case sensitivity, multiline matching, and so on.

The match succeeds Re.match method returns a matching object, otherwise none is returned.

We can use the group (NUM) or groups () matching object function to get a matching expression.

Matching Object Methods	Description
Group (num=0)	A string that matches the entire expression, group () can enter more than one group number at a time, in which case it returns a tuple that contains the corresponding values for those groups.
Groups ()	Returns a tuple containing all the group strings, from 1 to the included group number.

1 #-*-coding:utf-8-*-2  3 ImportRe4 Print(Re.match ('www','www.runoob.com'). span ())#match at start position5 Print(Re.match ('com','www.runoob.com'))#Do not match at start position

Results:

1 (0, 3)2 None

1 ImportRe2  3line ="Cats is smarter than dogs"4  5Matchobj = Re.match (r'(. *) is (. *?). *', line, re. m|Re. I)6  7 ifMatchobj:8    Print "Matchobj.group ():", Matchobj.group ()9    Print "Matchobj.group (1):", Matchobj.group (1)Ten    Print "Matchobj.group (2):", Matchobj.group (2) One Else: A    Print "No match!!"

Results:

1 Matchobj.group ():  Cats is smarter than dogs2 matchobj.group (1):  Cats3 matchobj.group (2):  Smarter

[Python Study Notes] Regular expressions