Python – When to use Absolute Path vs Relative Path in Python

absolute-pathpathpwdpythonrelative-path

For reference. The absolute path is the full path to some place on your computer. The relative path is the path to some file with respect to your current working directory (PWD). For example:

Absolute path:
C:/users/admin/docs/stuff.txt

If my PWD is C:/users/admin/, then the relative path to stuff.txt would be: docs/stuff.txt

Note, PWD + relative path = absolute path.

Cool, awesome. Now, I wrote some scripts which check if a file exists.

os.chdir("C:/users/admin/docs") os.path.exists("stuff.txt")

This returns TRUE if stuff.txt exists and it works.

Now, instead if I write,

os.path.exists("C:/users/admin/docs/stuff.txt")

This also returns TRUE.

Is there a definite time when we need to use one over the other? Is there a methodology for how python looks for paths? Does it try one first then the other?

Thanks!

Best Answer

If you don't know where the user will be executing the script from, it is best to compute the absolute path on the user's system using os and __file__.

__file__ is a global variable set on every Python script that returns the relative path to the *.py file that contains it.

import os
my_absolute_dirpath = os.path.abspath(os.path.dirname(__file__))

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Python – How to get an absolute file path in Python

>>> import os
>>> os.path.abspath("mydir/myfile.txt")
'C:/example/cwd/mydir/myfile.txt'

Also works if it is already an absolute path:

>>> import os
>>> os.path.abspath("C:/example/cwd/mydir/myfile.txt")
'C:/example/cwd/mydir/myfile.txt'

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Use the subprocess module in the standard library:

import subprocess
subprocess.run(["ls", "-l"])

The advantage of subprocess.run over os.system is that it is more flexible (you can get the stdout, stderr, the "real" status code, better error handling, etc...).

Even the documentation for os.system recommends using subprocess instead:

The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in the subprocess documentation for some helpful recipes.

On Python 3.4 and earlier, use subprocess.call instead of .run:

subprocess.call(["ls", "-l"])

Best Answer

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