Regex - Part 2

Searching an Occurrence of Pattern

re.search() method either returns None (if the pattern doesn't match) or a re.MatchObject
re.MatchObject contains information about the matching part of the string
method stops after the first match
best suited for testing a regular expression more than extracting data

import re 
# 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: 
	print ("Match at index %s, %s" % (match.start(), match.end())) 

	# "June 24" 
	print ("Full match: %s" % (match.group(0))) 

	# "June" 
	print ("Month: %s" % (match.group(1))) 

	# "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() function attempts to match pattern to whole string
function returns a match object on success, None on failure

syntax

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 (|).

example

# A Python program to demonstrate 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))) 
	
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() returns all non-overlapping matches of pattern as a list of strings
the string is scanned left-to-right
matches are returned in the order found

example

import re 
 
string = "Hello my Number is 123456789 and my friend's number is 987654321"

# find digits. 
regex = '\d+'			

match = re.findall(regex, string) 
print(match)

output

['123456789', '987654321']