Extracting extension from filename in Python

python

file-manipulation

pathlib

best-practices

byNikita Barsukov·Aug 8, 2024

To fetch a file's extension in Python, employ os.path.splitext(). This built-in function divides the filename at the final period, yielding a tuple where the second element encapsulates the extension with its preceding dot. Observe this illustrative code snippet:

from os.path import splitext

extension = splitext("example.txt")[1]
print(extension)  # Outputs: .txt

This single line of code is compact yet powerfully uncovers the lurking file extension .txt.

Python's Special Agent: `os.path.splitext()`

At the surface, os.path.splitext seems like another typical Python function. Yet, it's an unsung hero with specialized skills:

No fear of punctuation: Amply prepared for filenames like archive.tar.gz, ensuring an accurate split: ('.archive.tar', '.gz').
Dot-file awareness: Knows that files like .gitignore are dot-files with zero extension, hence cleverly returns: ('', '.gitignore').
Escapes directory dot-traps: When the filename path ambles across directories with periods, os.path.splitext() smoothly bypasses these and only targets the end file component.

Here's a not-so-secret formula to remove the leading dot:

extension = splitext("example.txt")[1][1:]
print(extension)  # Outputs: txt (the Mysterio of extensions without the domes and drones)

Even when a file extension isn't in the picture, os.path.splitext adeptly manages by supplying an empty string:

filename_no_ext, ext = splitext("README")
print(ext)  # Outputs: ''  (Empty...just like my coffee mug)

This ability to sidestep manual parsing is akin to the Pythonian principle: Simple is better than complex.

Metamorphosis with `pathlib`

For folks who fancy object-oriented styling, the pathlib module flaunts its .suffix and .stem methods.

from pathlib import Path

file_path = Path("example.tar.gz")
print(file_path.suffix)  # Outputs: .gz
print(file_path.stem)    # Outputs: example.tar

What's more — pathlib is fluent in dealing with numerous extensions:

print(file_path.suffixes)  # Outputs: ['.tar', '.gz']

This functionality makes handling extension-rich files like archive.tar.gz as breezy as an air conditioner in August.

`os.path` vs `pathlib`: The Showdown

When to utilize os.path.splitext and when to switch to pathlib?

Legacy code or minimal import requirements: Stick to os.path.splitext.
Modern best practices: Glide towards pathlib.
Working with multiple extensions: pathlib's .suffixes is your navigator.
Embracing object-oriented programming: pathlib is your ally.

These choices depend on your coding style, project needs, and environment constraints - they all resonate with Python's "There should be one-- and preferably only one --obvious way to do it" philosophy.

Beware Possible Pitfalls

As you journey through the realm of file manipulation, keep these cautionary notes handy:

Dot-file doppelgängers: Dot-files like .gitignore are not tagged with extensions.
Multiple-extension mazes: Files like archive.tar.gz present multiple layers that require pathlib's .suffixes for deft handling.
Confusing path dots: Directories with periods are potential decoys, but os.path.splitext skillfully evades them.