string = input("Gimme string: ")
valid = False
start = False
end = False

while not valid:
    if string[0:6] == "http://":
        start = True
    else:
        start = False
    if string[-4:] == ".com":
        end = True
    else:
        end = False
    valid = start and end
    if not valid:
        string = input("gimme good string: ")