when is filter test applied?
In the following code (python3):
for rb in filter (lambda b : b in some_seq, seq):
... some code that might modify some_seq
I'm assuming that the test 'b in some_seq' is applied late, at the start of
each iteration (but it doesn't seem to be working that way in my real code),
so that if 'some_seq' is modified during a previous iteration the test is
correctly performed on the latest version of 'some_seq' at the start of each
iteration. Is this correct, and is this guaranteed?