Need to restart runtime before import an installed package in Colab

I am trying to install and use an existing python package in Google Colab. For this, I download the code from Github in Colab and install the package, but when trying to import the installed package, I get a ModuleNotFoundError: No module named 'gem' Error.

However, if I restart the runtime and run the importing cell again, then no error appears.

I am wondering why I need to restart the runtime after installing the package and before importing.

Any clever response will be much appreciated.

My code is:

[1] !wget --show-progress --continue -O /content/gem.zip https://github.com/palash1992/GEM/archive/master.zip

[2] !unzip gem.zip

# Installing Dependencies
[3] ! pip install keras==2.0.2

[4] %cd GEM-master
!sudo python3 setup.py install
%cd-

[5] from gem.utils import graph_util, plot_util

And the error that I get is:

ModuleNotFoundError                       Traceback (most recent call last)
<ipython-input-5-af270a37878a> in <module>()
      1 import matplotlib.pyplot as plt
      2 
----> 3 from gem.utils import graph_util, plot_util
      4 from gem.evaluation import visualize_embedding as viz
      5 from gem.evaluation import evaluate_graph_reconstruction as gr

ModuleNotFoundError: No module named 'gem'

---------------------------------------------------------------------------
NOTE: If your import is failing due to a missing package, you can
manually install dependencies using either !pip or !apt.

To view examples of installing some common dependencies, click the
"Open Examples" button below.
---------------------------------------------------------------------------

However, if I restart the runtime using os.kill(os.getpid(), 9) after installing the package and before importing it, then the above error does not appear.

Solution

It seems that everything except simple !pip installs seem to not get included in colab's module registry except after a runtime restart. Likely, colab has a fairly naive way of keeping track of available modules. You also have to restart the runtime if you import a different version of a previously installed package.

Probably they just have a script that appends the metadata for piply installed packages to a list-like object during runtime. And imports just search from the top of the list (which is why the restart is required for diff versions of packages).

However, when a new runtime is started, the list-like registry is initialized and populated by searching the relevant directories.