Regular Expression in Python with Examples | Set 1
The module re provides support for regular expressions in Python. Below are main methods in this module.
Searching an occurrence of pattern
re.search() : This 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.
# 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." )
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Output :
Match at index 14, 21 Full match: June 24 Month: June Day: 24
Matching a Pattern with Text
re.match() : This function attempts to match pattern to whole string. The re.match function returns a match object on success, None on failure.
re.match(pattern, string, flags=0) pattern : Regular expression to be matched. string : String where pattern is searched flags : We can specify different flags using bitwise OR (|).
# A Python program to demonstrate working # of re.match(). import re
# a sample function that uses regular expressions # to find month and day of a date. def findMonthAndDate(string):
regex = r "([a-zA-Z]+) (\d+)"
match = re.match(regex, string)
if match = = None :
print ( "Not a valid date" )
return
print ( "Given Data: %s" % (match.group()))
print ( "Month: %s" % (match.group( 1 )))
print ( "Day: %s" % (match.group( 2 )))
# Driver Code findMonthAndDate( "Jun 24" )
print ("")
findMonthAndDate( "I was born on June 24" )
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Output:
Given Data: Jun 24 Month: Jun Day: 24 Not a valid date
Finding all occurrences of a pattern
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 (Source : Python Docs).
# 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)
# This example is contributed by Ayush Saluja. |
Output :
['123456789', '987654321']
Regular expression is a vast topic. It’s a complete library. Regular expressions can do a lot of stuff. You can Match, Search, Replace, Extract a lot of data. For example, below small code is so powerful that it can extract email address from a text. So we can make our own Web Crawlers and scrappers in python with easy.Look at the below regex.
# extract all email addresses and add them into the resulting set new_emails = set(re.findall(r"[a-z0-9\.\-+_]+@[a-z0-9\.\-+_]+\.[a-z]+", text, re.I))
We will soon be discussing more methods on regular expressions.