Is there an idiomatic way to add an extension using Python's Pathlib?

Question

I'm using Python's Pathlib and I want to take something like

p = Path('/path/to/foo')

And then try a couple of different extensions. I can do

for ext in ['.txt', '.md', '.note']
    filename = Path(str(p) + ext)

but that feels a little awkward. Is there a better way to do this?

Maybe you could use endswith() but it doesn't feel awkward to me. — Rob, Jul 16 '18 at 16:46
A format string could make this a little nicer: `filename = Path(f"{p}{ext}")` — phoenix, Sep 29 '21 at 10:42

user2357112 · Accepted Answer · 2020-03-24T00:57:14.137

111

The with_suffix method will return a new path with a different extension, either changing an existing extension or adding a new one. Examples from the docs:

>>> p = PureWindowsPath('c:/Downloads/pathlib.tar.gz')
>>> p.with_suffix('.bz2')
PureWindowsPath('c:/Downloads/pathlib.tar.bz2')
>>> p = PureWindowsPath('README')
>>> p.with_suffix('.txt')
PureWindowsPath('README.txt')

In your case, p.with_suffix(ext) would do the job.

For cases where you need to add a suffix after any existing suffixes instead of removing existing suffixes, you can use p.with_suffix(p.suffix+ext). This is kind of clunky, though, and I don't know whether I would prefer it over Path(str(p)+ext).

edited Mar 24 '20 at 00:57

answered Jul 16 '18 at 17:20

user2357112

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that's exactly what I wanted - it even replaces the suffix in the case of `foo.txt`, if I do `with_suffix('.md')` then it returns `foo.md`. Excellent! (also I was searching for "ext" or "extension" on the page, which apparently is why I missed that) – Wayne Werner Jul 16 '18 at 18:00
1

Nice, but what if you don't want to replace the existing suffix. Back to Path(str(path) + ".xyz")? – Mathieu Longtin Oct 04 '18 at 14:05
6

@MathieuLongtin: That, or `p.with_suffix(p.suffix+'.xyz')`. – user2357112 Oct 04 '18 at 14:35
That is better! Not great, but better. – Mathieu Longtin Oct 04 '18 at 18:13
I find `Path(f'{p}.xyz')` to be slightly better. – Jeyekomon Feb 07 '23 at 14:50

bitranox · Answer 2 · 2020-07-05T15:29:34.363

You might use pathlib3x - it offers a backport of the latest (at the date of writing this answer Python 3.10.a0) Python pathlib for Python 3.6 or newer, and a few additional functions like append_suffix

>>> python -m pip install pathlib3x

>>> import pathlib3x as pathlib

>>> pathlib.Path('some_path').append_suffix('.ext')
PosixPath('some_path.ext')

>>> pathlib.Path('some_path.ext.ext2').append_suffix('.ext3')
PosixPath('some_path.ext.ext2.ext3')

>>> pathlib.Path('some_path.ext').append_suffix('.tar.gz')
PosixPath('some_path.ext.tar.gz')

you can find it on github or PyPi

^{Disclaimer: I'm the author of the pathlib3x library.}

Is there an idiomatic way to add an extension using Python's Pathlib?

2 Answers2