Development with Python

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:$ mkdir -p ~/sites/$SITENAME/static
:$ mkdir -p ~/sites/$SITENAME/virtualenv
# you should replace the URL in the next line with the URL for your own repo
:$ git clone \
~/sites/$SITENAME/source
Resolving deltas: 100% [...]
A bash variable defined using export only lasts as long as that con‐
sole session. If you log out of the server and log back in again, you’ll
need to redefine it. It’s devious because Bash won’t error, it will just
substitute the empty string for the variable, which will lead to weird
results … if in doubt, do a quick echo $SITENAME.
Now we’ve got the site installed, let’s just try running the dev server—this is a smoke
test, to see if all the moving parts are connected:
:$ $ cd ~/sites/$SITENAME/source
$ python3 manage.py runserver
Traceback (most recent call last):
File "manage.py", line 8, in <module>
from django.core.management import execute_from_command_line
ImportError: No module named django.core.management
Ah. Django isn’t installed on the server.
Creating a Virtualenv
We could install it at this point, but that would leave us with a problem: if we ever wanted
to upgrade Django when a new version comes out, it would be impossible to test the
staging site with a different version from live. Similarly, if there are other users on the
server, we’d all be forced to use the same version of Django.
The solution is a “virtualenv”—a neat way of having different versions of Python pack‐
ages installed in different places, in their own “virtual environments”.
Let’s try it out locally, on our own PC first:
$ pip3 install virtualenv # will need a sudo on linux/macos.
We’ll follow the same folder structure as we’re planning for the server:
$ virtualenv --python=python3 ../virtualenv
$ ls ../virtualenv/
bin include lib
That will create a folder at ../virtualenv which will contain its own copy of Python and
pip, as well as a location to install Python packages to. It’s a self-contained “virtual”
Python environment. To start using it, we run a script called activate, whichwill change
the system path and the Python path in such a way as to use the virtualenv’s executables
and packages:
142 | Chapter 8: Testing Deployment Using a Staging Site