The dropwhile() and takewhile() functions are stateful filter functions. They start in one mode; the given predicate function is a kind of flip-flop that switches the mode. The dropwhile() function starts in reject mode; when the function becomes False, it switches to pass mode. The takewhile() function starts in pass mode; when the given function becomes False, it switches to reject mode. Since these are filters, they will consume the entire iterable.
We can use these to skip header or footer lines in an input file. We use the dropwhile() function to reject header rows and pass the remaining data. We use the takewhile() function to pass data and reject trailer rows. We'll return to the ...
