Virtualenv allows you to create a repeatable, isolated environment for your project and its dependencies, without worrying about what packages and versions are installed globally on your development machine. This is a standard tool for most python projects, but since arcpy is installed as a separate, global package, using virtual environments is a little more difficult.
There are a couple of approaches to tackling this problem; either adding a .pth file to the local virtualenv, or by using the
--system-site-packages flag. Both of these have some disadvantages–the first requires manual modification of the virtual environment and storing the
.pth file separately, and the second brings in all the global dependencies into your virtual environment.
A third possibility is to use the site module, which will allow us to selectively expose global packages to all of our virtual environments; this is the approach we’ll take.
Virtualenv is included in the standard library at 3.3, but if you’re still using python 2.7, you’ll need to install it separately:pip install virtualenv
Customizing Site Packages
arcpy is installed globally and isn’t available as an independent package, we need to allow access to it in our virtual environment. We can do this by creating a
sitecustomize.py file; this will allow us to specify a subset of the globally installed packages, and that subset will be included in every virtual environment we create. At a minimum, we need arcpy and numpy, but you can add additional packages if you need to.
First we’ll create a directory to hold our subset; it doesn’t matter where we put it or what its called, but for this example, it will be
We can add the required arcpy directories by copying the global
Desktop10.5.pth file; this is just a list of directories for python to search, and it looks like this:
To handle numpy, we create a link (
mklink from a windows
ln from gitbash) to the global directory; putting it all together, it looks like this:
Once this is done, our
arcpy_includes directory should look like:
Now we create a file called
C:/Python27/ArcGIS10.5/Lib (note that the documentation recommends placing
sitecustomize.py in the global
Lib/site-packages directory, but virtualenv won’t be able to find it there). The contents of the file are short:
And that’s it–now arcpy and numpy will be included in every virtual environment we create.
Using the Virtual Environment
To use the virtual environment in a project, just navigate to your project directory; the first time around, we need to create the virtual environment–by convention, we’ll put in a local folder called
venv. We may also want to to tell
virtualenv which version of python to use; it’s often the case that we’ll have multiple versions installed, especially if we’ve upgraded ArcGIS. We can do that using the
Once the virtual environment is created, we activate it (from a
cmd shell, you don’t need the
Now any additional dependencies we install will only be installed to our local virtual environment, and not pollute the global site-packages. To deactivate the environment, just do:deactivate comments powered by Disqus