Write Python Regular Expression to Match File Extension

Using Python, we can easily search for specific types of files from a mixed list of file names using regular expressions. For this, we need to import Python's built-in module called re using the import keyword.

The Regular expression or Regex is a special sequence of characters like \, *, ^, etc, which are used to search for a pattern in a string or a set of strings. It can detect the presence or absence of characters by matching them with a particular pattern and can also split a string into one or more substrings.

The following is a syntax to import the Regex module -

import re

Usage of 're.search()' function in Regex module

The re.search() is used to search for the first occurrence of a character or pattern in a string. If the search character is not found in the string, it will return None. If they give characters present in it will return -

• Match Object: This indicates that the search() function has found a match and returned a match object. The match object stores details about the match.
• span(): This will return the start index and end index values of the matched characters.
• match: This is the actual substring that was matched in the search.

Following is the syntax of the re.search() function from the regex module -

re.search(pattern, string, flags=0)

The following are the parameters of the re.search() function from the regex module -

• pattern: This is the regular expression to be matched
• string: This is the string that would be searched to match the pattern anywhere in the string.
• Flags: It is an optional parameter; different flags can be specified using bitwise OR (|).

Following is a basic example of the re.search() function from the regex module -

import re
s = "Welcome to Tutorialspoint"
res = re.search(r"o", s)
print(res)

Following is the output of the above code -

<re.Match object; span=(4, 5), match='o'>

Regular Expression to Match with File Extension

In the following example, we have a list of file names with various extensions. Using the regex module, we check if any file in the list ends with the .txt extension. If a match is found, the corresponding file name is printed -

The dollar symbol ($) is a metacharacter used in regular expressions to match the end of a string. It checks whether the string ends with the specified characters.

# import library 
import re 

# list of different types of file 
filenames = ["tp.html", "tutorial.xml", "tutorialspoint.txt", "tutorials_point.jpg"] 

for file in filenames: 
   # search given pattern in the line 
   match = re.search("\.txt$", file) 
   # if match is found 
   if match: 
      print("The file ending with .txt is -", file) 

Output

Following is the output of the above code -

The file ending with .txt is - tutorialspoint.txt