Python sleep() Function

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

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

Example 1: Python sleep() Method

import time

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

Output

Printed immediately.
Printed after 2.4 seconds.

Here's how this program works:

• "Printed immediately" is printed
• time.sleep(2.4) suspends execution for 2.4 seconds.
• "Printed after 2.4 seconds" is printed.

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.

Create a Digital Clock in Python

import time

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

Output

02:10:50 PM
02:10:51 PM
02:10:52 PM
02:10:53 PM
02:10:54 PM
... ... ...

In the above example, 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.

To learn more, visit digital clock in Python shell.

Multithreading in Python

Before talking about the sleep() method 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.

Example 3: Python multithreading

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

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()

Output

Hello
Hello
Hi
Hello
Hi
Hi

The above example 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 we might get different outputs.

To learn more about multithreading, visit Multithreading in Python.

Python time.sleep() in multithreaded programs

In case of single-threaded programs, sleep() suspends execution of the thread and process.

However, the method suspends a thread rather than the whole process in multithreaded programs.

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()

Output

Hello
Hi
Hello
Hi
Hello
Hello
Hi
Hi

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