Python Regular Expression (RegEx)

A regular expressions are commonly used in programming as a unique text string to search a pattern. A regular expression is a special text string for describing a search pattern to locate, match and manage text. Python is a great example of a programming language that utilizes RegEx and can be used directly from the command line to find lines of data in a file.

Python Regular Expression (RegEx) Module

Python has an already existing built-in package for regular expressions called re. This is used to find search patterns within a text and multiple regular expression functions.

Python Regular Expression (RegEx) Functions

The hardest part of regular expressions is learning the basic understanding of the syntax and how to properly operate the use of regular expressions to operate once you understand the basic syntax of how regular expression commands operate If you have used regular expressions for other programming languages then the learning curve will be not as sharp. However, programming languages and programs do share similarities but not all programming languages use the same regular expressions.

Python Regular Expression (RegEx) Metacharacter Meanings

Python Regular Expression (RegEx) Sets

Python Regular Expression (RegEx) Special Sequences

Python findall() Function

The Python finadall() function will return all matches that contain the data provided.

Input:

import re
search_text = "I love programming in Python to find text in large text documents by using the findall() function in Python. "
x = re.findall("Py", search_text)
print(f"By using the Python findall() function we will search Python and return the results: {x} ")

Output:

By using the Python findall() function we will search Python and return the results: ['Py', 'Py']

Let’s findall() with a search string that is not in the variable that’s being searched. It will return an empty list when no results are found.

Input:

import re
search_text = "I love programming in Python to find text in large text documents by using the findall() function in Python. "
x = re.findall("Java", search_text)
print(f"By using the Python findall() function we will search Java and return the results: {x} ")

Output:

By using the Python findall() function we will search Java and return the results: []

Python search() Function

The Python search() function will search the string for a match and return the match object if there’s a match. If there’s more than one match, the first occurrence will be returned if matched.

Python search() Function Example 1

The first Python search() function example will return a match if the specified characters are at the end of the string.

Input:

import re
search_text = "I love programming in Python to find text in large text documents by using the search() function in Python"
x = re.search("PythonZ", search_text)
print(f"By using the Python search() function we will search Python and return only the first result: {x} ")

Output:

By using the Python search() function we will search Python and return only the first result: <re.Match object; span=(100, 106), match='Python'>

Python search() Function Example 2

The second Python search function example is using the character B to return a match where the specified characters are present, but NOT at the beginning (or at the end) of a word.

Input:

import re
search_text = "I love programming in Python to find text in large text documents by using the search() function in Python"
x = re.search("Bthon", search_text)
print(f"By using the Python search() function we will search ython and return only the first result: {x} ")

Output:

By using the Python search() function we will search ython and return only the first result: <re.Match object; span=(24, 28), match='thon'>

Python sub() Function

The Python sub() function will find and replace matches with the text provided.

Input:

import re
search_text = "I love programming in Python to find text in large text documents by using the search() function in Python"
x = re.sub("Python", "Java", search_text)
print(f"By using the Python sub() function, we will replace Python with Java: {x} ")

Output:

By using the Python sub() function, we will replace Python with Java: I love programming in Java to find text in large text documents by using the search() function in Java