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Why you should be using pathlib

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When I discovered Python’s new pathlib module a few years ago, I initially wrote it off as being a slightly more awkward and unnecessarily object-oriented version of the os.path module. I was wrong. Python’s pathlib module is actually wonderful!

In this article I’m going to try to sell you on pathlib. I hope that this article will inspire you to use Python’s pathlib module pretty much anytime you need to work with files in Python.

Update: I wrote a follow-up article to address further comments and concerns that were raised after this one. Read this article first and then take a look at the follow-up article here.

    os.path is clunky

    The os.path module has always been what we reached for to work with paths in Python. It’s got pretty much all you need, but it can be very clunky sometimes.

    Should you import it like this?

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    import os.path
    
    BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
    TEMPLATES_DIR = os.path.join(BASE_DIR, 'templates')
    

    Or like this?

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    from os.path import abspath, dirname, join
    
    BASE_DIR = dirname(dirname(abspath(__file__)))
    TEMPLATES_DIR = join(BASE_DIR, 'templates')
    

    Or maybe that join function is too generically named… so we could do this instead:

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    from os.path import abspath, dirname, join as joinpath
    
    BASE_DIR = dirname(dirname(abspath(__file__)))
    TEMPLATES_DIR = joinpath(BASE_DIR, 'templates')
    

    I find all of these a bit awkward. We’re passing strings into functions that return strings which we then pass into other functions that return strings. All of these strings happen to represent paths, but they’re still just strings.

    The string-in-string-out functions in os.path are really awkward when nested because the code has to be read from the inside out. Wouldn’t it be nice if we could take these nested function calls and turn them into chained method calls instead?

    With the pathlib module we can!

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    from pathlib import Path
    
    BASE_DIR = Path(__file__).resolve().parent.parent
    TEMPLATES_DIR = BASE_DIR.joinpath('templates')
    

    The os.path module requires function nesting, but the pathlib modules' Path class allows us to chain methods and attributes on Path objects to get an equivalent path representation.

    I know what you’re thinking: wait these Path objects aren’t the same thing: they’re objects, not path strings! I’ll address that later (hint: these can pretty much be used interchangeably with path strings).

    The os module is crowded

    Python’s classic os.path module is just for working with paths. Once you want to actually do something with a path (e.g. create a directory) you’ll need to reach for another Python module, often the os module.

    The os module has lots of utilities for working with files and directories: mkdir, getcwd, chmod, stat, remove, rename, and rmdir. Also chdir, link, walk, listdir, makedirs, renames, removedirs, unlink (same as remove), and symlink. And a bunch of other stuff that isn’t related to the filesystems at all: fork, getenv, putenv, environ, getlogin, and system. Plus dozens of things I didn’t mention in this paragraph.

    Python’s os module does a little bit of everything; it’s sort of a junk drawer for system-related stuff. There’s a lot of lovely stuff in the os module, but it can be hard to find what you’re looking for sometimes: if you’re looking for path-related or filesystem-related things in the os module, you’ll need to do a bit of digging.

    The pathlib module replaces many of these filesystem-related os utilities with methods on the Path object.

    Here’s some code that makes a src/__pypackages__ directory and renames our .editorconfig file to src/.editorconfig:

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    import os
    import os.path
    
    os.makedirs(os.path.join('src', '__pypackages__'), exist_ok=True)
    os.rename('.editorconfig', os.path.join('src', '.editorconfig'))
    

    This code does the same thing using Path objects:

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    from pathlib import Path
    
    Path('src/__pypackages__').mkdir(parents=True, exist_ok=True)
    Path('.editorconfig').rename('src/.editorconfig')
    

    Notice that the pathlib code puts the path first because of method chaining!

    As the Zen of Python says, “namespaces are one honking great idea, let’s do more of those”. The os module is a very large namespace with a bunch of stuff in it. The pathlib.Path class is a much smaller and more specific namespace than the os module. Plus the methods in this Path namespace return Path objects, which allows for method chaining instead of nested string-iful function calls.

    Don’t forget about the glob module!

    The os and os.path modules aren’t the only filepath/filesystem-related utilities in the Python standard library. The glob module is another handy path-related module.

    We can use the glob.glob function for finding files that match a certain pattern:

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    from glob import glob
    
    top_level_csv_files = glob('*.csv')
    all_csv_files = glob('**/*.csv', recursive=True)
    

    The new pathlib module includes glob-like utilities as well.

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    from pathlib import Path
    
    top_level_csv_files = Path.cwd().glob('*.csv')
    all_csv_files = Path.cwd().rglob('*.csv')
    

    After you’ve started using pathlib more heavily, you can pretty much forget about the glob module entirely: you’ve got all the glob functionality you need with Path objects.

    pathlib makes the simple cases simpler

    The pathlib module makes a number of complex cases somewhat simpler, but it also makes some of the simple cases even simpler.

    Need to read all the text in one or more files?

    You could open the file, read its contents and close the file using a with block:

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    from glob import glob
    
    file_contents = []
    for filename in glob('**/*.py', recursive=True):
        with open(filename) as python_file:
            file_contents.append(python_file.read())
    

    Or you could use the read_text method on Path objects and a list comprehension to read the file contents into a new list all in one line:

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    from pathlib import Path
    
    file_contents = [
        path.read_text()
        for path in Path.cwd().rglob('*.py')
    ]
    

    What if you need to write to a file?

    You could use the open context manager again:

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    with open('.editorconfig') as config:
        config.write('# config goes here')
    

    Or you could use the write_text method:

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    Path('.editorconfig').write_text('# config goes here')
    

    If you prefer using open, whether as a context manager or otherwise, you could instead use the open method on your Path object:

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    from pathlib import Path
    
    path = Path('.editorconfig')
    with path.open(mode='wt') as config:
        config.write('# config goes here')
    

    Or, as of Python 3.6, you can even pass your Path object to the built-in open function:

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    from pathlib import Path
    
    path = Path('.editorconfig')
    with open(path, mode='wt') as config:
        config.write('# config goes here')
    

    Path objects make your code more explicit

    What do the following 3 variables point to? What do their values represent?

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    person = '{"name": "Trey Hunner", "location": "San Diego"}'
    pycon_2019 = "2019-05-01"
    home_directory = '/home/trey'
    

    Each of those variables points to a string.

    Those strings represent different things: one is a JSON blob, one is a date, and one is a file path.

    These are a little bit more useful representations for these objects:

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    from datetime import date
    from pathlib import Path
    
    person = {"name": "Trey Hunner", "location": "San Diego"}
    pycon_2019 = date(2019, 5, 1)
    home_directory = Path('/home/trey')
    

    JSON objects deserialize to dictionaries, dates are represented natively using datetime.date objects, and filesystem paths can now be generically represented using pathlib.Path objects.

    Using Path objects makes your code more explicit. If you’re trying to represent a date, you can use a date object. If you’re trying to represent a filepath, you can use a Path object.

    I’m not a strong advocate of object-oriented programming. Classes add another layer of abstraction and abstractions can sometimes add more complexity than simplicity. But the pathlib.Path class is a useful abstraction. It’s also quickly becoming a universally recognized abstraction.

    Thanks to PEP 519, file path objects are now becoming the standard for working with paths. As of Python 3.6, the built-in open function and the various functions in the os, shutil, and os.path modules all work properly with pathlib.Path objects. You can start using pathlib today without changing most of your code that works with paths!

    What’s missing from pathlib?

    While pathlib is great, it’s not all-encompassing. There are definitely a few missing features I’ve stumbled upon that I wish the pathlib module included.

    The first gap I’ve noticed is the lack of shutil equivalents within the pathlib.Path methods.

    While you can pass Path objects (and path-like objects) to the higher-level shutil functions for copying/deleting/moving files and directories, there’s no equivalent to these functions on Path objects.

    So to copy a file you still have to do something like this:

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    from pathlib import Path
    from shutil import copyfile
    
    source = Path('old_file.txt')
    destination = Path('new_file.txt')
    copyfile(source, destination)
    

    There’s also no pathlib equivalent of os.chdir.

    This just means you’ll need to import chdir if you ever need to change the current working directory:

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    from pathlib import Path
    from os import chdir
    
    parent = Path('..')
    chdir(parent)
    

    The os.walk function has no pathlib equivalent either. Though you can make your own walk-like functions using pathlib fairly easily.

    My hope is that pathlib.Path objects might eventually include methods for some of these missing operations. But even with these missing features, I still find it much more manageable to use “pathlib and friends” than “os.path and friends”.

    Should you always use pathlib?

    Since Python 3.6, pathlib.Path objects work nearly everywhere you’re already using path strings. So I see no reason not to use pathlib if you’re on Python 3.6 (or higher).

    If you’re on an earlier version of Python 3, you can always wrap your Path object in a str call to get a string out of it when you need an escape hatch back to string land. It’s awkward but it works:

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    from os import chdir
    from pathlib import Path
    
    chdir(Path('/home/trey'))  # Works on Python 3.6+
    chdir(str(Path('/home/trey')))  # Works on earlier versions also
    

    Regardless of which version of Python 3 you’re on, I would recommend giving pathlib a try.

    And if you’re stuck on Python 2 still (the clock is ticking!) the third-party pathlib2 module on PyPI is a backport so you can use pathlib on any version of Python.

    I find that using pathlib often makes my code more readable. Most of my code that works with files now defaults to using pathlib and I recommend that you do the same. If you can use pathlib, you should.

    If you’d like to continue reading about pathlib, check out my follow-up article called No really, pathlib is great.

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