Resolving dependencies in a directed acyclic graph with a topological sort

In this recipe, we will show an application of a well-known graph algorithm: topological sorting. Let's consider a directed graph describing dependencies between items. For example, in a package manager, before we can install a given package P, we may need to install dependent packages.

The set of dependencies forms a directed graph. With topological sorting, the package manager can resolve the dependencies and find the right installation order of the packages.

Topological sorting has many other applications. Here, we will illustrate this notion on real data from the Debian package manager. We will find the installation order of the required packages for IPython.

Getting ready

You need the python-apt package in order to build the package dependency graph. The package is available at https://pypi.python.org/pypi/python-apt/.

We also assume that this notebook is executed on a Debian system (such as Ubuntu). If you...