Python sleep()

Python sleep()#

The sleep() function suspends (waits) execution of the current thread for a given number of seconds.

Python has a module named time which provides several useful functions to handle time-related tasks. One of the popular functions among them is sleep().

The sleep() function suspends execution of the current thread for a given number of seconds.

Example 1: Python sleep()#

# Example 1: Python sleep()

import time

print("Printed immediately.")
time.sleep(2.4)
print("Printed after 2.4 seconds.")

# When you run the program, the output will be like below:

Printed immediately.
Printed after 2.4 seconds.

Explanation:

  • "Printed immediately" is printed

  • Suspends (Delays) execution for 2.4 seconds.

  • "Printed after 2.4 seconds" is printed.

As you can see from the above example, sleep() takes a floating-point number as an argument.

Before Python 3.5, the actual suspension time may be less than the argument specified to the time() function.

Since Python 3.5, the suspension time will be at least the seconds specified.

In the below program, we computed and printed the current local time inside the infinite while loop. Then, the program waits for 1 second. Again, the current local time is computed and printed. This process goes on.

Example 2: Python create a digital clock#

# Example 2: Python create a digital clock

import time

while True:
    localtime = time.localtime()
    result = time.strftime("%I:%M:%S %p", localtime)
    print(result)
    time.sleep(1)

# When you run the program, the output will be something like below:

07:33:39 PM
07:33:40 PM
07:33:41 PM
07:33:42 PM
07:33:43 PM
07:33:44 PM
07:33:45 PM
07:33:46 PM
07:33:47 PM
07:33:48 PM
07:33:49 PM
07:33:50 PM
07:33:51 PM
07:33:52 PM
07:33:53 PM
07:33:54 PM
07:33:55 PM
07:33:56 PM
07:33:57 PM
07:33:58 PM
07:33:59 PM
07:34:00 PM
07:34:01 PM
07:34:02 PM
07:34:03 PM
07:34:04 PM
07:34:05 PM
07:34:06 PM
07:34:07 PM
07:34:08 PM
07:34:09 PM
07:34:10 PM
07:34:11 PM
07:34:12 PM
07:34:13 PM
07:34:14 PM
07:34:15 PM
07:34:16 PM
07:34:17 PM
07:34:18 PM
07:34:19 PM
07:34:20 PM
07:34:21 PM
07:34:22 PM
07:34:23 PM
07:34:24 PM
07:34:25 PM
07:34:26 PM

---------------------------------------------------------------------------
KeyboardInterrupt                         Traceback (most recent call last)
<ipython-input-2-2f7f4e5fdb49> in <module>
      7     result = time.strftime("%I:%M:%S %p", localtime)
      8     print(result)
----> 9     time.sleep(1)
     10 
     11 # When you run the program, the output will be something like below:

KeyboardInterrupt:

Here is a slightly modified better version of the above program.

import time

while True:
    localtime = time.localtime()
    result = time.strftime("%I:%M:%S %p", localtime)
    print(result, end="", flush=True)
    print("\r", end="", flush=True)
    time.sleep(1)

07:34:55 PM

---------------------------------------------------------------------------
KeyboardInterrupt                         Traceback (most recent call last)
<ipython-input-3-76a0a5ce1450> in <module>
      6     print(result, end="", flush=True)
      7     print("\r", end="", flush=True)
----> 8     time.sleep(1)

KeyboardInterrupt:

To learn more, visit digital clock in Python shell.

Multithreading in Python#

Before talking about sleep() in multithreaded programs, let’s talk about processes and threads.

A computer program is a collection of instructions. A process is the execution of those instructions.

A thread is a subset of the process. A process can have one or more threads.

All the programs above in this article are single-threaded programs. Here’s an example of a multithreaded Python program.

Example 3: Python multithreading#

# Example 3: Python multithreading

import threading 
  
def print_hello_three_times():
    for i in range(3):
        print("Hello")

def print_hi_three_times(): 
    for i in range(3): 
        print("Hi") 

t1 = threading.Thread(target=print_hello_three_times)  
t2 = threading.Thread(target=print_hi_three_times)  

t1.start()
t2.start()

# When you run the program, the output will be something like below:

Hello
Hello
Hello
Hi
Hi
Hi

Explanation: The above program has two threads t1 and t2. These threads are run using t1.start() and t2.start() statements.

Note: that, t1 and t2 run concurrently and you might get different output.

Visit this page to learn more about Multithreading in Python.

time.sleep() in multithreaded programs#

The sleep() function suspends execution of the current thread for a given number of seconds.

In case of single-threaded programs, sleep() suspends execution of the thread and process. However, the function suspends a thread rather than the whole process in multithreaded programs.

Example 4: sleep() in a multithreaded program#

# Example 4: sleep() in a multithreaded program

import threading 
import time
  
def print_hello():
    for i in range(4):
        time.sleep(0.5)
        print("Hello")

def print_hi(): 
    for i in range(4): 
        time.sleep(0.7)
        print("Hi") 

t1 = threading.Thread(target=print_hello)  
t2 = threading.Thread(target=print_hi)  
t1.start()
t2.start()

Explanation: The above program has two threads. We have used time.sleep(0.5) and time.sleep(0.75) to suspend execution of these two threads for 0.5 seconds and 0.7 seconds respectively.

Recommended Reading: Python time.sleep() sleeps thread

Contents