如何使用time（）倒数

Question

I have made this code to make a Countdown:

import time
end = time.time() + 5.5
if time.time() == end:
    print('Time\'s up')

That didn't work. It wasn't an error. It didn't happened anything.Has anybody an idea? Thanks!

Answer 1

You check time.time() again immediately after setting end , and you only check it once, so it is definitely not going to be 5.5 seconds later. If you want to do this by making minimal modifications to your code:

while time.time() < end:
    pass
print('Time\'s up')

you don't want to check for == in case the exact microsecond is not returned by the call to time.time().

If you want to do this the right way, you should use time.sleep(5.5) .

Answer 2

You're comparing for equality, but that assumes that the timestamp returned is exactly the same as the original one, plus 5.5 seconds. That won't happen unless you're very lucky. Additionally you're doing this check right after you've retrieved the previous time, and there is no chance that 5.5 seconds will pass between those two statements.

You can fix this by either using the appropriate way - or the naive way.

The correct way to handle this is to use time.sleep(5.5) :

import time

time.sleep(5.5)
print("Time's up!")

The naive way to implement it like in your example:

import time
end = time.time() + 5.5

while time.time() < end:
    pass

print("Time's up")

This will spin an empty loop until the requested time has passed. The reason why I'm calling this naive is because your program will be stuck spending all available CPU resources while doing nothing, except for checking the clock and the current time until 5.5 seconds has passed. In the first example it tells the operating system that "Hey, wake me up in 5.5 seconds" and other processes can use the CPU in between.