The built-in filter() function uses a predicate to determine whether an item is passed or rejected. Instead of a function that calculates a value, we can use a second, parallel iterable to determine which items to pass and which to reject.
We can think of the filter() function as having the following definition:
def filter(function, iterable):
i1, i2 = tee(iterable, 2)
return compress(i1, map(function, i2))
We cloned the iterable using the tee() function. We'll look at this function in detail later. The map() function will generate results of applying the filter predicate function, function(), to each value in the iterable, yielding a sequence of True and False values. The sequence of Booleans are used to compress ...
