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Python exit commands: quit(), exit(), sys.exit() and os._exit()

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  • Last Updated : 13 Sep, 2022
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The functions quit(), exit(), sys.exit() and os._exit() have almost the same functionality as they raise the SystemExit exception by which the Python interpreter exits and no stack traceback is printed. We can catch the exception to intercept early exits and perform cleanup activities; if uncaught, the interpreter exits as usual. 

quit() function in Python

The quit() function works only if the site module is imported so it should not be used in production code. Production code means the code is being used by the intended audience in a real-world situation. This function should only be used in the interpreter. It raises the SystemExit exception behind the scenes. If you print it, it will give a message

Example: 

Python3




# Python program to demonstrate
# quit()
for i in range(10):
     
    # If the value of i becomes
    # 5 then the program is forced
    # to quit
    if i == 5:
         
        # prints the quit message
        print(quit)
        quit()
    print(i)

Output:

0
1
2
3
4
Use quit() or Ctrl-D (i.e. EOF) to exit

exit() function in Python 

The exit() is defined in site.py and it works only if the site module is imported so it should be used in the interpreter only. It is like a synonym for quit() to make Python more user-friendly. It too gives a message when printed: 

Example

Python3




# Python program to demonstrate
# exit()
for i in range(10):
    # If the value of i becomes
    # 5 then the program is forced
    # to exit
    if i == 5:
 
        # prints the exit message
        print(exit)
        exit()
    print(i)

Output:

0
1
2
3
4
Use exit() or Ctrl-D (i.e. EOF) to exit

sys.exit([arg]) using Python

Unlike quit() and exit(), sys.exit() is considered good to be used in production code for the sys module is always available. The optional argument arg can be an integer giving the exit or another type of object. If it is an integer, zero is considered “successful termination”. 
Note: A string can also be passed to the sys.exit() method. 

Example: 

Python3




# Python program to demonstrate
# sys.exit()
import sys
 
age = 17
 
# program that stops execution if the age is less than 18.
if age < 18:   
    # exits the program
    sys.exit("Age less than 18")   
else:
    print("Age is not less than 18")

Output:

An exception has occurred, use %tb to see the full traceback.

SystemExit: Age less than 18

os._exit(n) in Python

The os._exit() method in Python is used to exit the process with specified status without calling cleanup handlers, flushing stdio buffers, etc. 

Note: This method is normally used in the child process after os.fork() system call. The standard way to exit the process is sys.exit(n) method.

Python3




# Python program to explain os._exit() method
     
# importing os module
import os
     
# Create a child process
# using os.fork() method
pid = os.fork()
     
     
# pid greater than 0
# indicates the parent process
if pid > 0:
     
    print("\nIn parent process")
    # Wait for the completion
    # of child process and   
    # get its pid and
    # exit status indication using
    # os.wait() method
    info = os.waitpid(pid, 0)
     
         
    # os.waitpid() method returns a tuple
    # first attribute represents child's pid
    # while second one represents
    # exit status indication
     
    # Get the Exit code
    # used by the child process
    # in os._exit() method
         
    # firstly check if
    # os.WIFEXITED() is True or not
    if os.WIFEXITED(info[1]) :
        code = os.WEXITSTATUS(info[1])
        print("Child's exit code:", code)
     
else :
    print("In child process")
    print("Process ID:", os.getpid())
    print("Hello ! Geeks")
    print("Child exiting..")
         
    # Exit with status os.EX_OK
    # using os._exit() method
    # The value of os.EX_OK is 0       
    os._exit(os.EX_OK)

Output:

In child process
Process ID: 25491
Hello ! Geeks
Child exiting..

In parent process
Child's exit code: 0

Conclusion: Among the above four exit functions, sys.exit() is preferred mostly because the exit() and quit() functions cannot be used in production code while os._exit() is for special cases only when the immediate exit is required.


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