Handling time

Time in pySFML

Unlike many other libraries where time is an int number of milliseconds, or a float number of seconds, pySFML doesn’t impose any specific unit or type for time values. Instead it leaves this choice to the user through a flexible Time. All pySFML classes and functions that manipulate time values use this class.

Time wraps a relative time value (in other words, a time span). It is not a date-time class which would represent the current year/month/day/hour/minute/second, it’s just a value that represents a certain amount of time, and how to interpret it depends on the context where it is used.

Converting time

A Time value can be constructed from different source units: seconds, milliseconds and microseconds. There is a (non-member) function to turn each of them into a Time:

t1 = sf.microseconds(10000)
t2 = sf.milliseconds(10)
t3 = sf.seconds(0.01)

Note that these three times are all equal.

Similarly, a Time can be converted back to either seconds, milliseconds or microseconds:

time = ...

usec = time.microseconds # long
msec = time.milliseconds # int
sec = time.seconds       # float

Playing with time values

Time is just an amount of time, so it supports arithmetic operations such as addition, subtraction, comparison, etc. Times can also be negative.

t1 = ... t2 = t1 * 2 t3 = t1 + t2 t4 = -t3

b1 = t1 == t2 b2 = t3 > t4

Measuring time

Now that we’ve seen how to manipulate time values with pySFML, let’s see how to do something that almost every program needs: measuring the time elapsed.

pySFML has a very simple class for measuring time: Clock. It only has two members: elapsed_time, to retrieve the time elapsed since the clock started, and restart(), to restart the clock.

clock = sf.Clock() # starts the clock
# ...
elapsed1 = clock.elapsed_time
print(elapsed1.seconds)
clock.restart()
# ...
elapsed2 = clock.elapsed_time
print(elapsed2.seconds)

Note that restart also returns the elapsed time, so that you can avoid the slight gap that would exist if you had to call elapsed_time explicitly before restart. Here is an example that uses the time elapsed at each iteration of the game loop to update the game logic:

clock = sf.Clock()
while window.is_open:
   elapsed = clock.restart()
   update_game(elapsed)
   #...