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``? ``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 ``/usr/lib/python2.7/site-packages`` (or
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:
.. code:: python
$ 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
environment.
While creating the virtualenv you have to make a decision. Do you
want this virtualenv to use packages from your system ``site-packages``
or install them in the virtualenv’s site-packages? By default,
virtualenv will not give access to the global ``site-packages``.
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:
.. code:: python
$ virtualenv --system-site-packages mycoolproject
You can turn off the ``env`` by typing:
.. code:: python
$ deactivate
Running `python` after deactivating will use your system installation
of Python again.
**Bonus**
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