How can I make a time delay in Python? [duplicate]

Answer 1

asyncio.sleep

Notice in recent Python versions (Python 3.4 or higher) you can use asyncio.sleep. It's related to asynchronous programming and asyncio. Check out next example:

import asyncio
from datetime import datetime

@asyncio.coroutine
def countdown(iteration_name, countdown_sec):
    """
    Just count for some countdown_sec seconds and do nothing else
    """
    while countdown_sec > 0:
       print(f'{iteration_name} iterates: {countdown_sec} seconds')
       yield from asyncio.sleep(1)
       countdown_sec -= 1

loop = asyncio.get_event_loop()
tasks = [asyncio.ensure_future(countdown('First Count', 2)),
         asyncio.ensure_future(countdown('Second Count', 3))]

start_time = datetime.utcnow()

# Run both methods. How much time will both run...?
loop.run_until_complete(asyncio.wait(tasks))

loop.close()

print(f'total running time: {datetime.utcnow() - start_time}')

We may think it will "sleep" for 2 seconds for first method and then 3 seconds in the second method, a total of 5 seconds running time of this code. But it will print:

total_running_time: 0:00:03.01286

It is recommended to read asyncio official documentation for more details.

Answer 2

A bit of fun with a sleepy generator.

The question is about time delay. It can be fixed time, but in some cases we might need a delay measured since last time. Here is one possible solution:

Delay measured since last time (waking up regularly)

The situation can be, we want to do something as regularly as possible and we do not want to bother with all the last_time, next_time stuff all around our code.

Buzzer generator

The following code (sleepy.py) defines a buzzergen generator:

import time
from itertools import count

def buzzergen(period):
    nexttime = time.time() + period
    for i in count():
        now = time.time()
        tosleep = nexttime - now
        if tosleep > 0:
            time.sleep(tosleep)
            nexttime += period
        else:
            nexttime = now + period
        yield i, nexttime

Invoking regular buzzergen

from sleepy import buzzergen
import time
buzzer = buzzergen(3) # Planning to wake up each 3 seconds
print time.time()
buzzer.next()
print time.time()
time.sleep(2)
buzzer.next()
print time.time()
time.sleep(5) # Sleeping a bit longer than usually
buzzer.next()
print time.time()
buzzer.next()
print time.time()

And running it we see:

1400102636.46
1400102639.46
1400102642.46
1400102647.47
1400102650.47

We can also use it directly in a loop:

import random
for ring in buzzergen(3):
    print "now", time.time()
    print "ring", ring
    time.sleep(random.choice([0, 2, 4, 6]))

And running it we might see:

now 1400102751.46
ring (0, 1400102754.461676)
now 1400102754.46
ring (1, 1400102757.461676)
now 1400102757.46
ring (2, 1400102760.461676)
now 1400102760.46
ring (3, 1400102763.461676)
now 1400102766.47
ring (4, 1400102769.47115)
now 1400102769.47
ring (5, 1400102772.47115)
now 1400102772.47
ring (6, 1400102775.47115)
now 1400102775.47
ring (7, 1400102778.47115)

As we see, this buzzer is not too rigid and allow us to catch up with regular sleepy intervals even if we oversleep and get out of regular schedule.

Answer 3

If you would like to put a time delay in a Python script:

Use time.sleep or Event().wait like this:

from threading import Event
from time import sleep

delay_in_sec = 2

# Use time.sleep like this
sleep(delay_in_sec)         # Returns None
print(f'slept for {delay_in_sec} seconds')

# Or use Event().wait like this
Event().wait(delay_in_sec)  # Returns False
print(f'waited for {delay_in_sec} seconds')

However, if you want to delay the execution of a function do this:

Use threading.Timer like this:

from threading import Timer

delay_in_sec = 2

def hello(delay_in_sec):
    print(f'function called after {delay_in_sec} seconds')

t = Timer(delay_in_sec, hello, [delay_in_sec])  # Hello function will be called 2 seconds later with [delay_in_sec] as the *args parameter
t.start()  # Returns None
print("Started")

Outputs:

Started
function called after 2 seconds

Why use the later approach?

• It does not stop execution of the whole script (except for the function you pass it).
• After starting the timer you can also stop it by doing timer_obj.cancel().

Answer 4

How can I make a time delay in Python?

In a single thread I suggest the sleep function:

>>> from time import sleep

>>> sleep(4)

This function actually suspends the processing of the thread in which it is called by the operating system, allowing other threads and processes to execute while it sleeps.

Use it for that purpose, or simply to delay a function from executing. For example:

>>> def party_time():
...     print('hooray!')
...
>>> sleep(3); party_time()
hooray!

"hooray!" is printed 3 seconds after I hit Enter.

Example using sleep with multiple threads and processes

Again, sleep suspends your thread - it uses next to zero processing power.

To demonstrate, create a script like this (I first attempted this in an interactive Python 3.5 shell, but sub-processes can't find the party_later function for some reason):

from concurrent.futures import ThreadPoolExecutor, ProcessPoolExecutor, as_completed
from time import sleep, time

def party_later(kind='', n=''):
    sleep(3)
    return kind + n + ' party time!: ' + __name__

def main():
    with ProcessPoolExecutor() as proc_executor:
        with ThreadPoolExecutor() as thread_executor:
            start_time = time()
            proc_future1 = proc_executor.submit(party_later, kind='proc', n='1')
            proc_future2 = proc_executor.submit(party_later, kind='proc', n='2')
            thread_future1 = thread_executor.submit(party_later, kind='thread', n='1')
            thread_future2 = thread_executor.submit(party_later, kind='thread', n='2')
            for f in as_completed([
              proc_future1, proc_future2, thread_future1, thread_future2,]):
                print(f.result())
            end_time = time()
    print('total time to execute four 3-sec functions:', end_time - start_time)

if __name__ == '__main__':
    main()

Example output from this script:

thread1 party time!: __main__
thread2 party time!: __main__
proc1 party time!: __mp_main__
proc2 party time!: __mp_main__
total time to execute four 3-sec functions: 3.4519670009613037

Multithreading

You can trigger a function to be called at a later time in a separate thread with the Timer threading object:

>>> from threading import Timer
>>> t = Timer(3, party_time, args=None, kwargs=None)
>>> t.start()
>>>
>>> hooray!

>>>

The blank line illustrates that the function printed to my standard output, and I had to hit Enter to ensure I was on a prompt.

The upside of this method is that while the Timer thread was waiting, I was able to do other things, in this case, hitting Enter one time - before the function executed (see the first empty prompt).

There isn't a respective object in the multiprocessing library. You can create one, but it probably doesn't exist for a reason. A sub-thread makes a lot more sense for a simple timer than a whole new subprocess.

Answer 5

Delays are done with the time library, specifically the time.sleep() function.

To just make it wait for a second:

from time import sleep
sleep(1)

This works because by doing:

from time import sleep

You extract the sleep function only from the time library, which means you can just call it with:

sleep(seconds)

Rather than having to type out

time.sleep()

Which is awkwardly long to type.

With this method, you wouldn't get access to the other features of the time library and you can't have a variable called sleep. But you could create a variable called time.

Doing from [library] import [function] (, [function2]) is great if you just want certain parts of a module.

You could equally do it as:

import time
time.sleep(1)

and you would have access to the other features of the time library like time.clock() as long as you type time.[function](), but you couldn't create the variable time because it would overwrite the import. A solution to this to do

import time as t

which would allow you to reference the time library as t, allowing you to do:

t.sleep()

This works on any library.

Answer 6

There are five methods which I know: time.sleep(), pygame.time.wait(), matplotlib's pyplot.pause(), .after(), and driver.implicitly_wait().

---

time.sleep() example (do not use if using tkinter):

import time
print('Hello')
time.sleep(5) # Number of seconds
print('Bye')

---

pygame.time.wait() example (not recommended if you are not using the pygame window, but you could exit the window instantly):

import pygame
# If you are going to use the time module
# don't do "from pygame import *"
pygame.init()
print('Hello')
pygame.time.wait(5000) # Milliseconds
print('Bye')

---

matplotlib's function pyplot.pause() example (not recommended if you are not using the graph, but you could exit the graph instantly):

import matplotlib
print('Hello')
matplotlib.pyplot.pause(5) # Seconds
print('Bye')

---

The .after() method (best with Tkinter):

import tkinter as tk # Tkinter for Python 2
root = tk.Tk()
print('Hello')
def ohhi():
    print('Oh, hi!')
root.after(5000, ohhi) # Milliseconds and then a function
print('Bye')

---

Finally, the asyncio.sleep() method:

import asyncio
asyncio.sleep(5)