Adding a directory to sys.path with pathlib

Question

I'm trying to add a directory to PATH with code like this:

PROJECT_DIR = Path(__file__).parents[2]
sys.path.append(
 PROJECT_DIR / 'apps'
)

It doesn't work. If I do print sys.path I see something like this:

[..., PosixPath('/opt/project/apps')]

How should I fix this code? Is it normal to write str(PROJECT_DIR / 'apps')?

• hiro protagonist: why would you want to avoid using str?
• kharandziuk: I don't want to avoid this. I just ask what the proper way to use pathlib.
• vaultah: re. you second question (since it's not covered in answers): yes, it's normal. Documentation mentions str: The string representation of a path is the raw filesystem path itself (in native form, e.g. with backslashes under Windows), which you can pass to any function taking a file path as a string.

Answer 1

From the docs:

A program is free to modify this list for its own purposes. Only strings should be added to sys.path; all other data types are ignored during import.

Add the path as a string to sys.path:

PROJECT_DIR = Path(__file__).parents[2]
sys.path.append(
 str(PROJECT_DIR / 'apps')
)

PROJECT_DIR is an instance of PosixPath which has all the goodies like / and .parents etc. You need to convert it to a string if you want to append it to sys.path.

• florisla: You may want to resolve() the Path before adding it to sys.path. That makes it absolute -- file isnt't always absolute.
• hiro protagonist: @florisla as this is done at runtime there is no need for that (as long as you do not move the modules before they are imported).

Answer 2

Support for path-like-objects on sys.path is coming (see this pull request) but not here yet.

Answer 3

You could also use os.fspath. It return the file system representation of the path.

import os
 
PROJECT_DIR = Path(__file__).parents[2]
APPS_DIR = PROJECT_DIR / 'apps'
sys.path.append(os.fspath(APPS_DIR))

Documentation: https://docs.python.org/3/library/os.html#os.fspath

• wim: May as well just use str()

Answer 4

project_dir = os.path.join(os.path.abspath(os.path.dirname(__file__)),"..","..")
sys.path.append(os.path.join(project_dir,"apps"))
#or maybe you need it at the start of the path
sys.path.insert(0,os.path.join(project_dir,"apps"))

why are you using this weird pathlib library instead of pythons perfectly good path utils?

• hiro protagonist: may be a matter of taste - pathlib is pretty nice!
• vaultah: This does not answer the question.
• kharandziuk: I guess you miss this part .parents[2] in your answer
• hiro protagonist: @Joran Beasley: by all means leave the answer! os.path is a perfectly fine library indeed! and for python <3 none of the pathlib stuff will work.
• hiro protagonist: python love! (and: pathlib is builtin in python >3 and evidently backported to python 2.* [as mentioned by kharandziuk]).