The easiest way to get a file extension in python is splitext('filename') method from os module. This method returns a tuple that contains two values: filename (without extension) and its extension.

import os

file = "your/path/to/file.py"
file2 = "another/path/to/file.html"
file3 = "file.txt"

print(os.path.splitext(file))
print(os.path.splitext(file2))
print(os.path.splitext(file3))

Output:

('your/path/to/file', '.py')
('another/path/to/file', '.html')
('file', '.txt')
#python