virtualenv - How to recreate a virtual env in python

Question

I have installed virtualenv and virtualenvwrapper on Ubuntu 16.04 I have created one enviroment named env1

$ sudo apt-get install python-pip
$ pip install virtualenv
$ pip install --upgrade pip 
$ pip install virtualenvwrapper
$ export WORKON_HOME=~/Envs
$ mkdir -p $WORKON_HOME
$ source /usr/local/bin/virtualenvwrapper.sh
$ mkvirtualenv env1

Once in (env1) I have installed several packages

(env1) $ pip install numpy
(env1) $ pip install scipy
(env1) $ pip install matplotlib
(env1) $ apt-get install python-tk

I have also installed opencv3 (I am not copying how because is too long)

I am using env1 for a specific project.

Now I want to start another project using the same packages, but I also want to add other packages.

I have created env2, and I was wondering if it is possible to copy env1 to env2 without the need to re-install everything again from scratch.

Answer 1

Your best option is to do this:

virtualenv-1:

pip freeze > requirements.txt 

virtualenv-2:

pip install -r requirements.txt

Assuming they are both the on the same system and use the same Python, it is somewhat possible to just copy the site-packages:

cp -Rp /environments/virtualenv-1/lib/python2.7/site-packages 
       /environments/virtualenv-2/lib/python2.7/site-packages

This won't necessarily work though:

• some packages will install dependencies and other things into /bin/ or elsewhere. most don't, but many do.
• if the python versions for the virtualenvs differ -- even on a minor version -- that can break libraries that use c extensions.

So your best bet is to pip freeze and reinstall from that file.