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.

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 

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 (|). 

Python3

# 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")

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). 

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)

# 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.

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