Regular Expression In Python

In this article, we going to learn regular expressions with the “RE module”. This method allows you to search for a string, or within an array.

This lesson is suitable for the intermediate level if you are unfamiliar with the classes and functions it is not recommended to start this article, you can prepare it from the article here.

What is Re Module?

Re, short for Regular expression, is a python library. With the help of this module, in-sentence search recognition programs can be developed.

import re

x = re.compile("[a-e]")

print(x.findall("Hello, Mr. Mark")
Compile: ["e" , "a"]

As you can see, all the letters in the brackets section were searched in the sentence and added to the array when found.

The concept of “a – e” that we enter into gives us the letters a, b, c, d, and e. so we can use “a-e, b-d” instead of entering an array one by one.

Special Search Commands

The re module offers you many shortcuts. Now let’s look at the shortcuts used for numerical operations.

import re

x = re.compile("\d")

print(x.findall("Year 2021"))

y = re.compile("\d+")

print(y.findall("Year 2021"))
Output: [2 , 0 , 2 , 1]
Output: [2021]

If you do not put +, each letter will get a different index, if you put +, the combined numbers will be calculated as a single index.

There are many shortcuts like this one. Let’s check the other shortcuts. You can use all shortcuts in the same way.

import re

x = re.compile("\w")
y = re.compile("\w+")
z = re.compile("\W")

print(x.findall("Hi, Welcome"))
print(x.findall("Hi, Welcome"))
print(z.findall("Hi, Welcome..."))
output: ["H" , "i" , "," , "W" , "e" , "l" , "c" , "o" , "m" , "e"
output: ["Hi" , "Welcome"]
output: ["," , "..."]

Replace Method

With the “*” operator, the last letter you typed replaces the * operator, so you can get a complete string with the same as the last letter.

import re

x = re.compile('xyz*')

Output: ['xyz', 'xyzzzzz']

As you can see * is assigned as continuous z so all the letters z are added to the string. Let’s move on to a new function now.

Split Function

The first function we learned was finding the concepts for us. This function is to find and manipulate those concepts.

from re import split

print(split("W+" , "Hi, my name is ..."))
print(split("d+" , "this year is 2021"))
Output: ["Hi" , "my" , "name" , "is"]
Output: ["this" , "year" , "is"]

Sub Function

It is used to replace, an expression with another expression, very similar to the other function, it saves the modified version instead of deleting it from the string.

from re import sub

print(sub("th" , "--" , "this book")) #case sensitive
print(sub("th" , "**" , "This book" , flags = re.IGNORECASE)) 
Output: --is book
Output: **is book

Escape Function

It is an adjustment tool, it fills the spaces with “\”. It works with other escape characters, for example, it fills the tab space you create.

from re import escape

print(escape("this is program"))
print(escape("this \t is \t program"))
Output: this\ is\ program
Output: this\ \ \ is\ \ \ program

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