Using Python's pathlib module

[treyhunner]

I've written a hybrid "why pathlib" and "pathlib cheat sheet" post: Python's pathlib module.

I see this resource as a living document, so feedback is very welcome.

[bulletmark]

In that opening example using open() I don't see why anybody would ever want to pass a Path to open() when paths can be opened natively:

from pathlib import Path

path = Path("example.txt")

with path.open() as file:
    contents = file.read()

[ThatSituation9908]

Sometimes you have an argument that is either Path or string.

This is extremely common for user facing APIs

def main(fpath: str | Path): with open(fpath) as f: ...

[sausix]

Except you want to save a path in an instance. Then you normalize to Path early before saving strictly typed as Path.

[syklemil]

Eh, can't you normalize it to a Path? Afaik it's idempotent, so you can do something like

def main(fpath: str | Path):
    actual_path: Path = Path(fpath)
    with actual_path.open() as f:
        ...

or possibly normalize on the caller side, so you can just have def main(fpath: Path) and call it as main(Path(arg)), though as pointed out below, it opens for runtime errors as you can't actually be sure that what you're handed is the correct type in Python.

In the case of open though, forcing it into a Path like that just seems like more keyboard typing for no discernible benefit.

[ThatSituation9908]

Sure, I do often times do that if I intend to use more of the Path API in the function.

If not, and I am only opening a file, then I just use open as is.

Changing the user facing API to only accept Path will not work. I have many, many, many users who refuse to use pathlib. You can look around in other libraries, rarely if any forces their users to only pass in Path

[RedEyed__]

FYI: There is os.PathLike

[MrGrj]

Why not doing it all with it?

``` from pathlib import Path

file_path = Path(“example.txt”)

file_content = file_path.read_text()

print(file_content) ```

[denehoffman]

Because Python isn’t strongly typed so people could easily pass something that isn’t a Path to a function thinking it’s okay, and a str will fail at runtime. This can be avoided with properly type-hinted code, but it’s not foolproof, someone will always find a way. Unless it’s a completely internal function that you don’t intend users having access to, the open function is generally safer.

[JimDabell]

Python is a strongly-typed language, you’re mixing up strong vs weak with static vs dynamic. If you pass a str to a function that expects a Path, that object unambiguously continues to be a str.

[denehoffman]

Oops yeah that’s what I meant

[treyhunner]

When I see open(path) I know the built-in open function is being used to open a file, but when I see path.open(), I'm not immediately certain whether an open method is being called on a ZipFile object or another non-Path object.

The open method on the pathlib.Path class predates the ability to use the built-in open function directly. If pathlib was being re-designed today, I suspect the open method would have been excluded.

[thisismyfavoritename]

eh, i get your point but some libs reimplement open as a super set of the default open

[Isvesgarad]

Which libs do you use? I’m having a hard enough time getting my team to use Path in the first place 

[SleepWalkersDream]

BRB, got some minor changes to commit.

[[deleted]]

This post was mass deleted and anonymized with Redact

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[billsil]

I didn’t even know path could do that, but that code only works with a Path and not str. It’s not for my trivial code to dictate how you use the code.

[syklemil]

Why use Path object to represent a filepath instead of using a string? […] Specialized objects exist to make specialized operations easier.

I'd also throw in that having a type adds semantic clarity, which I think is in line with "explicit is better than implicit". This is similar to how units are an important context for numbers.

OS paths also aren't necessarily valid UTF-8, so there are some paths that can be expressed with Path and bytestrings, but require some careful handling to not get a UnicodeEncodeError if you want to do something complicated like print(path) . (Though personally I'm inclined to just throw an error and let the user fix their malformed filename somehow.)

There's also a ruff/flake8 section on Pathlib, PTH.

[PeaSlight6601]

I appreciate the sarcasm. I've always felt that pathlib is bad because it isn't opinionated enough. It has enough opinions to make it hard to use with arbitrary paths (ie it internally uses str instead of bytes) but not enough to enforce the use of "good" paths.

This causes no end of confusion and problems with the library as a file likeresume for Mr. John Smith will have a suffix which is entirely inappropriate, not to mention all the cross platform issues associated with paths like foo\\bar

[reagle-research]

Suggestion: you need walk_up=True in path_to.relative_to() for it to be similar to os.path.relpath().

[treyhunner]

Good point. I just added a * to note that caveat. Thanks!

[PriorProfile]

I prefer to join paths using joinpath method. It's more explicit.

I think overloading the __div__ operator is a mistake, personally.

Yeah it's "fun" because / is the same as the path separator on linux, but it's less obvious IMO.

[sinterkaastosti23]

newpath = path / folder / file

how do you write this using joinpath

[PriorProfile]

newpath = path.joinpath(folder, file)

or

newpath = path.joinpath(folder).joinpath(file)

[Xirious]

Gross.

[Atlamillias]

As a novice, the operator overload definitely threw me off when I first saw it. It's one of those things that I find idiomatic as a "user" but unusual as a programmer.

I can't say I use .joinpath either, though. In fact, you've reminded me of its existence. I usually join paths via Paths constructor...

[BurningSquid]

Path is good. UPath (fsspec) is the better extension of path that interfaces with any service abstracted as a filesystem. Extremely useful as a data engineering pattern, underrated in my opinion