The core of functional programming is the use of pure functions to map values from the input domain to the output range. A pure function has no side effects, a relatively easy threshold for us to achieve in Python.
Avoiding side effects also means reducing our dependence on variable assignment to maintain the state of our computations. We can't purge the assignment statement from the Python language, but we can reduce our dependence on stateful objects. This means we need to choose among the available Python built-in data structures to select those that don't require stateful operations.
This chapter will present several Python features from a functional viewpoint, as follows: