Prerequisite: Regular Expression with Examples | Python
A Regular expression (sometimes called a Rational expression) is a sequence of characters that define a search pattern, mainly for use in pattern matching with strings, or string matching, i.e. “find and replace”-like operations. Regular expressions are a generalized way to match patterns with sequences of characters.
Module Regular Expressions (RE) specifies a set of strings (pattern) that matches it. To understand the RE analogy, MetaCharacters are useful, important and will be used in functions of module re.
There are a total of 14 metacharacters and will be discussed as they follow into functions:
\ Used to drop the special meaning of character
following it (discussed below)
[] Represent a character class
^ Matches the beginning
$ Matches the end
. Matches any character except newline
? Matches zero or one occurrence.
| Means OR (Matches with any of the characters
separated by it.
* Any number of occurrences (including 0 occurrences)
+ One or more occurrences
{} Indicate number of occurrences of a preceding RE
to match.
() Enclose a group of REs
re.search()
re.search() method either returns None (if the pattern doesn’t match), or a re.MatchObject that contains information about the matching part of the string. This method stops after the first match, so this is best suited for testing a regular expression more than extracting data.
Example:
Python3
# A Python program to demonstrate working of re.match(). import re # Lets use a regular expression to match a date string # in the form of Month name followed by day number regex = r"([a-zA-Z]+) (\d+)" match = re.search(regex, "I was born on June 24") if match != None: # We reach here when the expression "([a-zA-Z]+) (\d+)" # matches the date string. # This will print [14, 21), since it matches at index 14 # and ends at 21. print("Match at index % s, % s" % (match.start(), match.end())) # We us group() method to get all the matches and # captured groups. The groups contain the matched values. # In particular: # match.group(0) always returns the fully matched string # match.group(1) match.group(2), ... return the capture # groups in order from left to right in the input string # match.group() is equivalent to match.group(0) # So this will print "June 24" print("Full match: % s" % (match.group(0))) # So this will print "June" print("Month: % s" % (match.group(1))) # So this will print "24" print("Day: % s" % (match.group(2))) else: print("The regex pattern does not match.") |
Output:
Match at index 14, 21 Full match: June 24 Month: June Day: 24
re.findall()
Return all non-overlapping matches of pattern in string, as a list of strings. The string is scanned left-to-right, and matches are returned in the order found.
Example:
Python3
# A Python program to demonstrate working of # findall() import re # A sample text string where regular expression # is searched. string = """Hello my Number is 123456789 and my friend's number is 987654321""" # A sample regular expression to find digits. regex = '\d+' match = re.findall(regex, string) print(match) |
Output:
['123456789', '987654321']
