I know how to set it in my /etc/profile and in my environment variables.
But what if I want to set it during a script? Is it import os, sys? How do I do it?
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5 Answers
You don't set PYTHONPATH, you add entries to sys.path. It's a list of directories that should be searched for Python packages, so you can just append your directories to that list.
import sys
sys.path.append('/path/to/whatever')
In fact, sys.path is initialized by splitting the value of PYTHONPATH on the path separator character (: on Linux-like systems, ; on Windows).
You can also add directories using site.addsitedir, and that method will also take into account .pth files existing within the directories you pass. (That would not be the case with directories you specify in PYTHONPATH.)
3 Comments
wecsam
It has been many years since this answer was posted, but I still want to add that if you want to make sure that Python checks the new directory before all of the others when importing, you should put the new directory first in the list, as in
sys.path.insert(0, '/path/to/whatever').
Breno
Is it "ok" to run
sys.path.insert(0, os.getcwd())?
tumbleweed
@Breno: The danger of inserting the
. (CWD) into the import path is that if you run your program in an untrusted directory, it can import things from there and execute them.You can get and set environment variables via os.environ:
import os
user_home = os.environ["HOME"]
os.environ["PYTHONPATH"] = "..."
But since your interpreter is already running, this will have no effect. You're better off using
import sys
sys.path.append("...")
which is the array that your PYTHONPATH will be transformed into on interpreter startup.
Comments
If you put sys.path.append('dir/to/path') without check it is already added, you could generate a long list in sys.path. For that, I recommend this:
import sys
import os # if you want this directory
try:
sys.path.index('/dir/path') # Or os.getcwd() for this directory
except ValueError:
sys.path.append('/dir/path') # Or os.getcwd() for this directory
5 Comments
PartialOrder
Nice. Very Pythonic.
Schütze
How can I empty the PythonPath? I don't want to append. I want to empty it and put what I only want inside. Is there a way to do this?
Thayz
Did you try re-initialising it by calling sys.path.__init__()? This should empty python path. Hope this helps.
user7610
@francisco-manuel-garca-botella Answering old questions is very welcome on this site! Nothing to be sorry for.
markgalassi
I disagree that this is pythonic, and I would suggest that it is not a good programming approach. Excception handling is very expensive when the exception happens, so you don't want to use it to replace an "if" statement where it's quite possible that you will use the else. A simple if 'mypath' in sys.path ... else ... would be my advice.
PYTHONPATH ends up in sys.path, which you can modify at runtime.
import sys
sys.path += ["whatever"]
you can set PYTHONPATH, by os.environ['PATHPYTHON']=/some/path, then you need to call os.system('python') to restart the python shell to make the newly added path effective.
1 Comment
tripleee
os.system() doesn't "restart the python shell", it starts a new interactive Python instance. When you return from that, you're back in the calling script.