Core Python Programming

filter()

The second built-in function we examine in this chapter is filter(). Imagine going to an orchard and leaving with a bag of apples you picked off the trees. Wouldn't it be nice if you could run the entire bag through a filter to keep just the good ones? That is the main premise of the filter() function.

Given a sequence of objects and a “filtering” function, run each item of the sequence through the filter, and keep only the ones that the function returns true for. The filter() function calls the given Boolean function for each item of the provided sequence. Each item for which filter() returns a non-zero (true) value is appended to a list. The object that is returned is a “filtered” sequence of the original.

If we were to code filter() ...