Extracting extension from filename in Python

Question

Is there a function to extract the extension from a filename?

Answer 1

For simple use cases one option may be splitting from dot:

>>> filename = "example.jpeg"
>>> filename.split(".")[-1]
'jpeg'

No error when file doesn't have an extension:

>>> "filename".split(".")[-1]
'filename'

But you must be careful:

>>> "png".split(".")[-1]
'png'    # But file doesn't have an extension

Also will not work with hidden files in Unix systems:

>>> ".bashrc".split(".")[-1]
'bashrc'    # But this is not an extension

For general use, prefer os.path.splitext

Answer 2

For funsies... just collect the extensions in a dict, and track all of them in a folder. Then just pull the extensions you want.

import os

search = {}

for f in os.listdir(os.getcwd()):
    fn, fe = os.path.splitext(f)
    try:
        search[fe].append(f)
    except:
        search[fe]=[f,]

extensions = ('.png','.jpg')
for ex in extensions:
    found = search.get(ex,'')
    if found:
        print(found)

Answer 3

With splitext there are problems with files with double extension (e.g. file.tar.gz, file.tar.bz2, etc..)

>>> fileName, fileExtension = os.path.splitext('/path/to/somefile.tar.gz')
>>> fileExtension 
'.gz'

but should be: .tar.gz

The possible solutions are here

Answer 4

Any of the solutions above work, but on linux I have found that there is a newline at the end of the extension string which will prevent matches from succeeding. Add the strip() method to the end. For example:

import os.path
extension = os.path.splitext(filename)[1][1:].strip() 

Answer 5

worth adding a lower in there so you don't find yourself wondering why the JPG's aren't showing up in your list.

os.path.splitext(filename)[1][1:].strip().lower()

Answer 6

filename='ext.tar.gz'
extension = filename[filename.rfind('.'):]