Stop command in python

Python exit command (quit(), exit(), sys.exit())

Let us check out the exit commands in python like quit(), exit(), sys.exit() commands.

Python quit() function

In python, we have an in-built quit() function which is used to exit a python program. When it encounters the quit() function in the system, it terminates the execution of the program completely.

It should not be used in production code and this function should only be used in the interpreter.

for val in range(0,5): if val == 3: print(quit) quit() print(val)

After writing the above code (python quit() function), Ones you will print “ val ” then the output will appear as a “ 0 1 2 “. Here, if the value of “val” becomes “3” then the program is forced to quit, and it will print the quit message.

You can refer to the below screenshot python quit() function.

Python exit() function

We can also use the in-built exit() function in python to exit and come out of the program in python. It should be used in the interpreter only, it is like a synonym of quit() to make python more user-friendly

for val in range(0,5): if val == 3: print(exit) exit() print(val)

After writing the above code (python exit() function), Ones you will print “ val ” then the output will appear as a “ 0 1 2 “. Here, if the value of “val” becomes “3” then the program is forced to exit, and it will print the exit message too.

You can refer to the below screenshot python exit() function.

Python sys.exit() function

In python, sys.exit() is considered good to be used in production code unlike quit() and exit() as sys module is always available. It also contains the in-built function to exit the program and come out of the execution process. The sys.exit() also raises the SystemExit exception.

import sys marks = 12 if marks < 20: sys.exit("Marks is less than 20") else: print("Marks is not less than 20")

After writing the above code (python sys.exit() function), the output will appear as a “ Marks is less than 20 “. Here, if the marks are less than 20 then it will exit the program as an exception occurred and it will print SystemExit with the argument.

You can refer to the below screenshot python sys.exit() function.

Python os.exit() function

So first, we will import os module. Then, the os.exit() method is used to terminate the process with the specified status. We can use this method without flushing buffers or calling any cleanup handlers.

import os for i in range(5): if i == 3: print(exit) os._exit(0) print(i)

After writing the above code (python os.exit() function), the output will appear as a “ 0 1 2 “. Here, it will exit the program, if the value of ‘i’ equal to 3 then it will print the exit message.

You can refer to the below screenshot python os.exit() function.

Python raise SystemExit

The SystemExit is an exception which is raised, when the program is running needs to be stop.

for i in range(8): if i == 5: print(exit) raise SystemExit print(i)

After writing the above code (python raise SystemExit), the output will appear as “ 0 1 2 3 4 “. Here, we will use this exception to raise an error. If the value of ‘i’ equal to 5 then, it will exit the program and print the exit message.

You can refer to the below screenshot python raise SystemExit.

Program to stop code execution in python

To stop code execution in python first, we have to import the sys object, and then we can call the exit() function to stop the program from running. It is the most reliable way for stopping code execution. We can also pass the string to the Python exit() method.

import sys my_list = [] if len(my_list) < 5: sys.exit('list length is less than 5')

After writing the above code (program to stop code execution in python), the output will appear as a “ list length is less than 5 “. If you want to prevent it from running, if a certain condition is not met then you can stop the execution. Here, the length of “my_list” is less than 5 so it stops the execution.

You can refer to the below screenshot program to stop code execution in python.

Difference between exit() and sys.exit() in python

• exit() – If we use exit() in a code and run it in the shell, it shows a message asking whether I want to kill the program or not. The exit() is considered bad to use in production code because it relies on site module.
• sys.exit() – But sys.exit() is better in this case because it closes the program and doesn’t ask. It is considered good to use in production code because the sys module will always be there.

In this Python tutorial, we learned about the python exit command with example and also we have seen how to use it like:

• Python quit() function
• Python exit() function
• Python sys.exit() function
• Python os.exit() function
• Python raise SystemExit
• Program to stop code execution in python
• Difference between exit() and sys.exit() in python

I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.

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How Do You End Scripts in Python?

Programming means giving instructions to a computer on how to perform a task. These instructions are written using a programming language. An organized sequence of such instructions is called a script.

As a programmer, your main job is to write scripts (i.e. programs). However, you also need to know how scripts can end. In this article, we will go over different ways a Python script can end. There is no prerequisite knowledge for this article, but it is better if you are familiar with basic Python terms.

If you are new to programming or plan to start learning it, Python is the best way to start your programming adventure. It is an easy and intuitive language, and the code is as understandable as plain English.

Scripts are written to perform a task; they are supposed to end after the task is completed. If a script never ends, we have a serious problem. For instance, if there is an infinite while loop in the script, the code theoretically never ends and might require an external interruption.

It is important to note that an infinite while loop might be created on purpose. A script can be written to create a service that is supposed to run forever. In this case, the infinite loop is intentional and there is no problem with that.

The end of a Python script can be frustrating or satisfying, depending on the result. If the script does what it is supposed to do, then it’s awesome. On the other hand, if it ends by raising an exception or throwing an error, then we will not be very happy.

5 Ways to End Python Scripts

Let’s start with the most common and obvious case: a script ends when there are no more lines to execute.

1. All the Lines Are Executed

The following is a simple script that prints the names in the list, along with the number of characters they contain:

mylist = ["Jane", "John", "Ashley", "Matt"] for name in mylist: print(name, len(name))

Jane 4 John 4 Ashley 6 Matt 4

The script does its job and ends. We all are happy.

Python scripts, or scripts in any other programming language, can perform a wide range of operations. In many cases, we cannot visually check the results. For instance, the job of a script might be reading data from a database, doing a set of transformations, and writing the transformed data to another database.

In scripts that perform a series of operations, it’s a good practice to keep a log file or add print statements after each individual task. It lets us do simple debugging in case of a problem. We can also check the log file or read the output of print statements to make sure the operation was completed successfully.

2. Uncaught Exception

It usually takes several iterations to write a script that runs without an error; it’s rare to get it right the first time. Thus, a common way that a script ends is an uncaught exception; this means there is an error in the script.

When writing scripts, we can think of some possible issues and place try-except blocks in the script to handle them. These are the exceptions that we are able to catch. The other ones can be considered uncaught exceptions.

Consider the following code:

mylist = ["Jane", "John", 2, "Max"] for i in mylist: print(f"The length of is ")

The length of Jane is 4 The length of John is 4 Traceback (most recent call last): File "", line 4, in TypeError: object of type 'int' has no len()

The code prints the length of each item in the list. It executes without a problem until the third item, which is an integer. Since we cannot apply the len function to an integer, the script throws an error and ends.

We can make the script continue by adding a try-except block.

mylist = ["Jane", "John", 2, "Max"] for i in mylist: try: print(f"The length of is ") except TypeError: print(f" does not have a length!")

The length of Jane is 4 The length of John is 4 2 does not have a length! The length of Max is 3

What does this try-except block do?

• It prints the f-string that includes the values and their lengths.
• If the execution in the try block returns a TypeError, it is caught in the except block.
• The script continues the execution.

The script still ends, but without an error. This case is an example of what we explained in the first section.

3. sys.exit()

The sys module is part of the Python standard library. It provides system-specific parameters and functions.

One of the functions in the sys module is exit , which simply exits Python. Although the exit behavior is the same, the output might be slightly different depending on the environment. For instance, the following block of code is executed in the PyCharm IDE:

import sys number = 29 if number < 30: sys.exit() else: print(number)

Process finished with exit code 0

Now, let’s run the same code in Jupyter Notebook:

import sys number = 29 if number < 30: sys.exit() else: print(number)

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

The sys.exit function accepts an optional argument that can be used to output an error message. The default value is 0, which indicates successful termination; any nonzero value is an abnormal termination.

We can also pass a non-integer object as the optional argument:

import sys number = 29 if number < 30: sys.exit("The number is less than 30.") else: print(number)

An exception has occurred, use %tb to see the full traceback. SystemExit: The number is less than 30.

The sys.exit() function raises the SystemExit exception, so the cleanup functions used in the final clause of a try-except-finally block will work. In other words, we can catch the exception and handle the necessary cleanup operations or tasks.

4. exit() and quit()

The exit() and quit() functions are built into Python for terminating a script. They can be used interchangeably.

The following script prints the integers in the range from 0 to 10. If the value becomes 3, it exits Python:

for i in range(10): print(i) if i == 4: exit()

0 1 2 3 Process finished with exit code 0

Note: The exit() function also raises an exception, but it is not intercepted (unlike sys.exit() ). Therefore, it is better to use the sys.exit() function in production code to terminate Python scripts.

5. External Interruption

Another way to terminate a Python script is to interrupt it manually using the keyboard. Ctrl + C on Windows can be used to terminate Python scripts and Ctrl + Z on Unix will suspend (freeze) the execution of Python scripts.

If you press CTRL + C while a script is running in the console, the script ends and raises an exception.

Traceback (most recent call last): File "", line 2, in KeyboardInterrupt

We can implement a try-except block in the script to do a system exit in case of a KeyboardInterrupt exception. Consider the following script that prints the integers in the given range.

for i in range(1000000): print(i)

We may want to exit Python if the script is terminated by using Ctrl + C while its running. The following block of code catches the KeyboardInterrupt exception and performs a system exit.

for i in range(1000000): try: print(i) except KeyboardInterrupt: print("Program terminated manually!") raise SystemExit

Program terminated manually! Process finished with exit code 0

We have covered 5 different ways a Python script can end. They all are quite simple and easy to implement.

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