How to Wait in Python  

Multiple operations happen simultaneously in an application to give the user a seamless browsing experience. However, some operations must be paused until an external condition is met, either on the user or server side. The ongoing operation is delayed for a moment until the external condition is met. So programmers who foresaw this eventuality in advance would tweak the program, such as directing it to wait until a specified time. Today, we will go through the wait() function and other methods in Python that are used to tell a computer to wait until a condition is met. 

What is Wait in Python? 

Though there are a plethora of ways to make a pause in Python the most prevalent way is to use the wait() function.

The wait() method in Python is used to make a running process wait for another function to complete its execution, such as a child process, before having to return to the parent class or event. This wait() method in Python is an os module method that synchronises the parent and child processes, implying that the parent will stand in line for the child process to complete its execution, i.e., wait until the child process ends before continuing with its process execution.

The wait() method is known as a method of the event class in the Python threading module to release the execution of an event when its internal flag is set to false, which will cause the current block or event to be released until the internal flag is set to true.

The wait() function is called os.wait() in Python, and its syntax is as follows:

Syntax:

os.wait()

This syntax returns the id of the child process as a tuple, coupled with a 16-bit number that also appears in the tuple to indicate the exit status. This method returns a 16-bit integer with higher and lower bytes, where the lower byte is represented by the signal number zero, which ends the process, and the higher byte contains the exit status notice. There are no parameters or arguments for the os.wait() function.

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How to Wait in Python?

The parent process is suspended or terminated until the child process completes its execution using the os.wait() technique. This wait() function is often used to wait for anything to happen in a process, and it will stand in line until the function is invoked true with certain conditions or modes specified.

The wait() function is defined in two separate modules in Python.

• os module
• threading module

The threading module’s event class contains a wait() method that suspends the current thread’s execution while the event is executed or completed. The os module accomplishes the same thing, but it collaborates with the parent process to ensure that the child process completes its execution. Let’s take a closer look at both of these tactics with some examples.

Some criteria necessitate that a Python program waits before continuing. To give the user a better experience, we may need to complete another function or load a file. Some methods for accomplishing this are discussed below.

Different Methods and Approaches 

We look at the following methods and approaches

1. Time Module
2. simple input()
3. os. wait()
4. event.wait()
5. Keyboard module
6. Code module
7. OS module

Python Time Module

• A Simple Sleep Function

Time is a module in Python. This module contains several useful functions for managing time-related tasks. Sleep() is one such function that returns a void after suspending the calling thread’s execution for seconds. The parameter might be a floating-point number to indicate more accurate sleep time. This is the most commonly utilized method because of its ease of use and platform independence. 

Example:

import time

print("project printed immediately.")
time.sleep(5.5)

print("project printed after 5.5 secs.")

• Sleep Function in Multithreaded Programming 

In multithreaded Python programmes, the sleep() function halts the current thread for a defined number of seconds rather than the entire process. In single-threaded systems, the sleep() method halts the thread and the process as a whole.

Example:

import threading
import time
  
def print_project():
    for i in range(5):

        time.sleep(1)
        print("project")
  
def print_natural():
    for i in range(5):
        #the current thread is suspended
        time.sleep(1.5)
        print("natural")
  

t1 = threading.Thread(target=print_project)
t2 = threading.Thread(target=print_natural)
t1.start()
t2.start()

Using simple input()

The input() function helps gather information from users. However, we may use this function to pause a Python script until a specific key is pressed, as shown in the following code:

Example:

print("project immediately")
i = input("Press Enter to continue: ")

print("project after the input.")

Using os. wait() 

The os. wait() function instructs the parent process to wait until the child process has completed its objectives. This is well explained in the following code:

Example:

import os
pr = os.fork()
if pr is 0:    
    print("Child process will print the numbers from the range 0 to 5")
    for i in range(0, 5):
        print("Child process of %d"%(i))      
    print("Child process of %d existing" %os.getpid())
    print("Process",(os.getpid()))

else:    

    print("Waiting")
    pro= os.wait()
    print("Child process of %d is executed" % (pro[0]))
    print("Parent process of %d is executed" % (os.getpid()))
    print("The parent process is", (os.getpid()))

Using event.wait()

When we want a thread to wait for an event, we can use the wait() method on the event object whose internal flag is set to false, which will block the thread until the set() method sets the internal flag of that event object to true. The thread is not blocked if the internal flag is true on entry. 

The thread is halted until the internal flag remains false or the timeout occurs. With the help of the timeout argument, we can provide the method with an optional timeout.

Using keyboard module

We can resume the program using this module by pressing the key provided in the Python script (in this case, the space key). The keyboard module is not included with Python and must be installed separately using the following command:

pip install keyboard

Example:

import keyboard

def pause():
    while True:
        if keyboard.read_key() == 'space':
            break
  
  
print("project was printed before using the pause")
pause()
print("project was printed after using pause")

Using code module

There is a function named interact in this module (). This straightforward solution may appeal to some non-programmers. As a result, the interpreter behaves almost identically to a genuine interpreter. If reading is specified, this creates a new instance of Interactive Console and sets dreadful as the InteractiveConsole.raw input() method.

Using OS module

system(“pause”) is a method in the OS module. We can have a Python application wait till a key is pressed using this method. However, this approach is platform-specific, meaning it only works on Windows. As a result, it isn’t commonly used.

Example:

import os
  
print("project printed immediately.")
os.system("pause")
print("project.")

Sleep in Python

The sleep() function is also like the wait() function which is used to halt a certain part of the program. 

The sleep() function in Python’s time module suspends the execution of a programme for a set period of time. This means that the application will be paused for the specified amount of time before being executed automatically.

There are instances when it is necessary to interrupt the flow of a program to allow for several other executions or simply because of the utility required. In this case, sleep() can be helpful since it gives a precise and flexible mechanism to halt code flow for any amount of time. This function discusses the function’s insight.

Syntax:

time.sleep(t)

Here t refers to the number of seconds execution to be suspended.

Return Value:

This method does not return any value.

Example 1:

import time
from threading import Thread

class programmer(Thread):
    def run(self):
        for x in range(0, 11):
            print(x)
            time.sleep(1)


class developer(Thread):
    def run(self):
        for x in range(200, 203):
            print(x)
            time.sleep(5)


print("Start thread")
programmer().start()
print("developer Thread")
developer().start()
print("Done")

Example 2:

Here time.sleep() is used in a multithreaded program

import threading 
import time
  
def print_program():
  for i in range(5):
    time.sleep(0.7)
    print("Program")
  
def print_tryout(): 
    for i in range(5): 
      time.sleep(0.9)
      print("Tryout") 

t1 = threading.Thread(target=print_program)  
t2 = threading.Thread(target=print_tryout)  
t1.start()
t2.start()

Example 3:

import time

time.sleep(7)

yourtuple = ('Liam Hemsworth', ' Dennis Ritchie', ' Linus Torvalds',
           'Tim Berners-Lee', 'Anders Hejlsberg',
           'Bjarne Stroustrup', 'James Gosling', 'Guido van Rossum')
 
print(yourtuple)

Conclusion

Some processes must be halted over an extended period while another process completes its tasks to accomplish a specific action. We hope you learned about the different ways to make a Python process wait in this article.

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