What should be my python packages path for a user

问题:

I'm on Mac OS X and I've heard that to avoid global installation of packages (using sudo) that might cause problems with the python files that OS X uses, the path to install python packages must be different than that of OS X.

Currently python executables are installed in :

/usr/local/bin/

Pip installs modules over here :

/usr/local/lib/python2.7/site-packages

Python is used from here :

/usr/local/bin/python

Are these paths safe?

回答1:

If you are on OS X, you should also have Python in /usr/bin:

$ which -a python
/usr/local/bin/python
/usr/bin/python

If you are using brew, the first python should be a symlink:

$ ls -hl $(which python)
lrwxr-xr-x  1 user  admin    34B Jun 23 16:53 /usr/local/bin/python -> ../Cellar/python/2.7.11/bin/python

If you are not using brew, you will have to explain to us how you installed a second version of python.

You should also have at least two site-packages:

$ find /usr -name 'site-packages'
/usr/local/Cellar/python/2.7.11/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
/usr/local/lib/python2.7/site-packages

If you installed python using brew, you should also have pip:

$ which pip
/usr/local/bin/pip

You should probably upgrade that to the latest pip:

$ pip install --upgrade pip

It should be safe to install python packages using /usr/local/bin/pip because they will be installed in /usr/local/lib/python2.7/site-packages. The /usr/local path is specifically for local software. Also, brew installs its files to /usr/local, so if you are using brew, you are already installing files there.

I am not sure why some folks say not to install any packages globally. I have never seen a reference that explained why this was a bad idea. If multiple users need the same package, it makes more sense to install it globally.

When I first started using virtualenv, it did not always work the way I expected it to. I had a machine with multiple users that needed requests, and because of problems with virtualenv, I wound up installing it globally using pip.

Both virtualenv and pip have improved a lot since I first started using them and I can see how using them can prevent some problems. If you are developing new software that needs the latest version of a package, virtualenv allows you to install the package without affecting the rest of the system. However, I still do not see why it is a bad idea to install packages globally.

回答2:

You shouldn't be mucking about with Python package paths, and you shouldn't be installing Python packages globally at all. Use a virtualenv for each project, and let pip install the libraries locally inside the virtualenv.

回答3:

I suggest you to make use of virtual environments, you can learn more about them here: http://docs.python-guide.org/en/latest/dev/virtualenvs/

to sum up

1. Create a virtual environment (venv): $ virtualenv venv

This creates a copy of Python in whichever directory you ran the command in placing it in a folder named venv.

2. Activate the virtual environment: $ source venv/bin/activate
3. Install packages with pip: $ pip install requests
4. When you are done deactivate the virtual environment: $ deactivate

回答4:

There are a number of options you can take, the easiest (as others have suggested) is virtualenv. Hopefully that's already installed if not, this is one of the few modules you should install globally. If you have Python 3.4+, you "should" have venv module (which is similar to virtualenv, but it's maintained by the Python team).

python2

virtualenv ~/.py-venvs/python2

python3

python3 -m venv ~/.py-venvs/python3

You could install modules to the local user using pip, but I'm not sure how well this is supported these days though:

pip install --user requests

You could also append directories to the $PYTHONPATH bash variable, but this should only be done as a last resort and under parental supervision :D. Try the other methods before this one.