Can someone explain to me what is happening in this python code?

Question

def stringParser():
    while True:
        name = yield
        (fname, lname) = name.split()
        f.send(fname)
        f.send(lname)

def stringLength():
    while True:
        string = yield
        print("Length of '{}' : {}".format(string, len(string)))


f = stringLength(); next(f)

s = stringParser()
next(s)
s.send('Jack Black')

And how did we get the output as

Length of 'Jack' : 4
Length of 'Black' : 5