11. Virtual Environment¶
Have you ever heard of
virtualenv? If you are a beginner,
then you might not have heard about it but if you are a
seasoned programmer then it may well be a vital part of your toolset.
So what is
Virtualenv is a tool which allows us to
make isolated python environments. Imagine you have an application that
needs version 2 of a library, but another application requires
version 3. How can you use and develop both these applications?
If you install everything into
whatever your platform’s standard location is), it’s easy to end up in a
situation where you unintentionally upgrade a package.
In another case, imagine that you have an application which is fully developed and you do not want to make any change to the libraries it is using but at the same time you start developing another application which requires the updated versions of those libraries.
What will you do? Use
virtualenv! It creates isolated environments
for your python application and allows you to install Python libraries
in that isolated environment instead of installing them globally.
To install it, just type this command in the shell:
$ pip install virtualenv
The most important commands are:
$ virtualenv myproject
$ source bin/activate
This first one makes an isolated virtualenv environment in the
myproject folder and the second command activates that isolated
While creating the virtualenv you have to make a decision. Do you
want this virtualenv to use packages from your system
or install them in the virtualenv’s site-packages? By default,
virtualenv will not give access to the global
If you want your
virtualenv to have access to your systems
site-packages, use the
--system-site-packages switch when creating
your virtualenv like this:
$ virtualenv --system-site-packages mycoolproject
You can turn off the
env by typing:
Running python after deactivating will use your system installation of Python again.
You can use
smartcd which is a library for bash and zsh and allows
you to alter your bash (or zsh) environment as you cd. It can be really
helpful to activate and deactivate a
virtualenv when you change
directories. I have used it quite a lot and love it. You can read more
about it on GitHub
This was just a short intro to virtualenv. There’s a lot more to it; this link has more information.