Regular Expressions in Python | Set 2 (Search, Match and Find All)

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.

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# 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 p attern is searched
flags : We can specify different flags 
        using bitwise OR (|). 
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# 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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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).

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# 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.

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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 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.

This article is contributed by Shwetanshu Rohatgi. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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