How to install from virtualenv only?

Question

I'm confused about virtualenv. I've been reading docs and trying examples, but its not getting better.

I created a virtualenv in the following way:

$ virtualenv myapp_venv --no-site-package

I used --no-site-packages because I want to know that that my requirements.txt is sufficient for building and running my code. I don't want to depend on whatever may be installed on my dev machine.

Then I try to install dependencies into my virtualenv:

$ source myapp_venv/bin/activate
(myapp_venv) $ sudo pip install -r requirements.txt

At this point I get a number of messages like this:

Requirement already satisfied (use --upgrade to upgrade): Flask==0.10.1 in /usr/local/lib/python2.7/dist-packages (from -r requirements.txt (line 1))

This surprises me, as I thought virtualenv would not be concerned with globally available packages, but with the environment of this project.

When I proceed to try to run the application:

(myapp_venv) $ python run.py
Traceback (most recent call last):
  File "run.py", line 1, in <module>
    from app import app
  File "/home/eric/code/python/tournament/app/__init__.py", line 1, in <module>
    from flask import Flask
ImportError: No module named flask

But if I deactivate the virtualenv, the app runs just fine.

How can I git pip to install the packages into the virtualenv?

For context, I'm professionally experienced with Java/Maven. I have a bit of Python language experience, but the Python ecosystem is still new to me.

Answer 1

Skip the sudo, and you will be fine. Sudo is telling to install globally.

Answer 2

Check no-global-site-packages.txt in your lib.

If no-global-site-packages.txt file is in lib folder, then It will take all packages from your virtualenv else It will take globally.

Also, As wissam said, don't use sudo. It is correct. because using sudo, It will install globally.