How can I get the file extension from a filename in Python?

General Discussions
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1

I’m working with files in Python and I need a way to extract the extension from a given filename. For example, if I have example.txt, I want to get "txt" as the result.

Is there a built-in function or a recommended approach to python get file extension?

Here’s a simple example of what I’m trying to achieve:

filename = "document.pdf"
# I want to extract "pdf" from this

What’s the cleanest and most reliable way to do this in Python, especially when filenames might contain multiple dots or no extension at all?

2

This is the method I use most often. It splits the filename into the root and the extension:

import os

filename = "document.pdf"
root, ext = os.path.splitext(filename)
print(ext)        # Output: '.pdf'
print(ext[1:])    # Output: 'pdf' (without the dot)

It’s safe even if the filename has multiple dots, like archive.tar.gz:

filename = "archive.tar.gz"
root, ext = os.path.splitext(filename)
print(ext)        # Output: '.gz'

Note that splitext only gives the last extension. If you need all parts, you might need extra handling.

3

I like this one for cleaner, object-oriented code:

from pathlib import Path

filename = Path("document.pdf")
print(filename.suffix)       # Output: '.pdf'
print(filename.suffix[1:])   # Output: 'pdf'

# For multiple extensions, use .suffixes
filename = Path("archive.tar.gz")
print(filename.suffixes)     # Output: ['.tar', '.gz']

This approach is especially nice if you’re already using pathlib for other file operations.

4

If you just want something simple and your filenames are well-formed:

filename = "document.pdf"
ext = filename.split('.')[-1]
print(ext)  # Output: 'pdf'

It works for most cases, but beware if the filename has no extension or starts with a dot (.gitignore).

Tip: I usually recommend os.path.splitext for compatibility or pathlib for modern Python code. They handle edge cases better than manual splitting.