Python Regular Expressions

Regular Expressions

Many times a lot of data would be stored in files and we may have to pick and change only relevant portions from a file. Even though there are string functions which allow us to manipulate strings, when dealing with more complicated requirements, we would need more powerful tools.

Regular Expressions are used to check and extract relevant portions of a string based on a pattern and modify if required.

Python has a module named 're' for regular expressions.

Working with 're' module

Two commonly used methods in the 're' module are search and sub. Search is used to find a pattern and sub is used to perform a substitution.

input_data = “Flight Savana Airlines a2134”

Here, r in front of the search pattern indicates 'raw string' where the special characters are treated as normal characters.

The output will be 'None' if the pattern is not found.

If you want to search the pattern “Air” in the given string “Airline” here are few example for that.

//Example 1:
import re
	if(re.search(r"Air","Airline")!=None):
		print("Pattern found")
	else:
		print("Pattern not found")
		
Output:
	Pattern found

//Example 2:
	import re
	if(re.search(r"Air","airline")!=None):
		print("Pattern found")
	else:
		print("Pattern not found")
		
Output:
	Pattern not found

More on regular expressions

Go through metacharacters and the respective examples given below.

re - Replacing data

We can use the function ‘sub’ to perform a substitution.

Go through the below example :

import re
	flight_details="Flight Savana Airlines a2134"
	print(flight_details)
	print(re.sub(r"Flight",r"Plane",flight_details))

Output:
Flight Savana Airlines a2134
Plane Savana Airlines a2134