Time based for loop in Python

Sure. Here's an iterator that gives you the time since start over and over until it reaches the end:

def time_counter(seconds):
    starttime = time.time()
    while True:
        now = time.time()
        if now > starttime + seconds:
            break
        yield now - starttime

for t in time_counter(20):
    print(t)
    time.sleep(3)

When I run this, it outputs:

9.5367431640625e-07
3.002220869064331
6.0040669441223145
9.004395961761475
12.006848812103271
15.009617805480957
18.011652946472168

If you need some different value, just change the yield expression.

If you don't need any value… then you don't need a for statement; your existing code is already perfectly readable, and a for loop that iterates over and discards some meaningless values is just going to make it confusing.

From https://wiki.python.org/moin/ForLoop

When do I use for loops? For loops are traditionally used when you have a piece of code which you want to repeat n number of times. As an alternative, there is the WhileLoop, however, while is used when a condition is to be met, or if you want a piece of code to repeat forever, for example -

The while loop feels more natural for this task, because the for needs an enumerable or a generator.

But if you really want to do it with a for loop, I guess you can construct a generator that yields something until time.time()<endtime:

def there_is_more_time(e)
    while time.time() < e:
        yield True

for i in there_is_more_time(endtime):
    do something

But as you see, you are again using while behind the scenes.

Perhaps someone can manage to not use the while inside the generator, but what's the point of doing so?

Perhaps you want to create a scheduler object?

https://docs.python.org/2/library/sched.html

import sched, time
s = sched.scheduler(time.time, time.sleep)

def print_time(): 
    print "From print_time", time.time()

def print_some_times():
    print time.time()
    s.enter(1, 1, print_time, ())
    s.enter(2, 1, print_time, ())
    s.enter(3, 1, print_time, ())
    s.enter(4, 1, print_time, ())
    s.enter(5, 1, print_time, ())
    s.run()
    print time.time()

Output:

1430392956.35
From print_time 1430392957.35
From print_time 1430392958.35
From print_time 1430392959.35
From print_time 1430392960.35
From print_time 1430392961.35
1430392961.35