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 CodefindMonthAndDate("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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