Quit exit разница python

The Many Ways to Exit in Python

It’s fundamentally useful to exit your program when it’s done. Here are five(!) ways to do so in Python.

1. raise SystemExit()

We can exit from Python code by raising a SystemExit exception:

The top level interpreter catches this special exception class and triggers its exit routine. This includes such steps as running all atexit functions, deleting all objects, and finally calling the OS exit function.

SystemExit optionally takes an integer for the exit code, where 0 represents success and any other value represents failure. We can use this to signal calling programs that an error occurred:

(When Python crashes with an exception, it uses an exit code of 1.)

If you’re looking for a quick answer, you can stop reading here. Use raise SystemExit(&LTcode>) as the obviousest way to exit from Python code and carry on with your life.

More obscurely, we can pass SystemExit any object, in which case Python will print the str() of that object to stderr and return an exit code of 1:

This can be handy, but I’d argue being explicit is clearer:

We can also call sys.exit() to exit Python, optionally with an exit code:

Underneath this only does raise SystemExit(<arg>) (in C).

Whilst sys.exit() is a little less typing than raise SystemExit() , it does require the import, which is a bit inconvenient. Also it hides the detail that an exception is raised.

3. exit() and quit()

exit() and quit() are “extra builtins” added by Python’s site module. Both essentially call raise SystemExit() , optionally with an exit code, like:

This looks super convenient! We don’t need to import anything, and the names are very short.

Unfortunately, the site module is optional. We can be skip loading it by running Python with the -S flag. In which case our call to quit() or exit() can still exit, but with a NameError exception:

 python -S -c ", line 1, in <module> 

Because exit() and quit() are optional, I’d recommend avoiding using them in your programs. But they’re fine to use at the REPL, which is why they exist. They even print usage information when written without brackets, to help new users trying to exit the REPL:

4. Ctrl-D (from the REPL)

Ctrl-D is the universal keyboard shortcut for exit. It sends EOF (End of File) to the current program, telling it the user is done sending input and it should exit.

Ctrl-D works with every command line program, including python . So it’s best to learn this shortcut, rather than use the Python-specific exit() . Then you can exit bash , zsh , ipython , sqlite , and any other command line program, without giving it a second thought.

5. os._exit()

The os._exit(n) function exits Python immediately with the given exit code n . It does so by calling the underlying OS exit function directly.

Unlike raising SystemExit , using os._exit() prevents Python from running its normal exit process. This is very destructive and usually undesirable, hence the “private/danger” underscore prefx.

The only reason I’ve found for calling os._exit() is when debugging in cases where raising SystemExit doesn’t work. For example, in a thread, raising SystemExit does not exit the progarm — it only stops the thread. Directly calling os._exit() can stop the entire program, which can be combined with a few well-placed debug prints to inspect state.

So, it’s worth knowing that os._exit() exists, although you should avoid it in day-to-day life.

✨Bonus✨ 6. Directly calling the OS exit function

os._exit() is a thin wrapper around our OS’ underlying exit function. We can call this function directly through Python’s ctypes module. This doesn’t confer any advantage — in fact it’s worse, because our code won’t work on all OSs. But it’s cool to know about.

On Linux/macOS/other Unixes, the exit function is available in the C standard library as exit() . We see its details by running man 3 exit — the Linux man page is online here. We can call it with ctypes like so:

Fin

Thanks to Anthony Sottile for the tip to use raise SystemExit(. ) in this video.

I hope you have found the exit you’re looking for,

Make your development more pleasant with Boost Your Django DX.

One summary email a week, no spam, I pinky promise.

Tags: python © 2021 All rights reserved. Code samples are public domain unless otherwise noted.

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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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4 Ways of Exiting the Program with Python Exit Function

There are many times when we want to exit from the program before the interpreter does so, and for this purpose, we have python exit function. Apart from exit we also have some functions like quit(), sys.exit() and os._exit(). Let’s learned about each of their advantages and disadvantages.

During a simple execution of the program (without the use of the functions mentioned above), when the interpreter reaches the end of the program/script, it exits from the program. But when we use functions like exit and quit, it gets out automatically at that time.

Working with Python Exit Functions

Sometimes we need the program to stop before the interpreter reaches the end of the script, like if we encounter something which is not required. So, let’s understand what functions can be used below in 4 ways –

1. Python Exit()

This function can only be implemented when the site.py module is there (it comes preinstalled with Python), and that is why it should not be used in the production environment. It should only be used with the interpreter.

In the background, the python exit function uses a SystemExit Exception. It means that when the interpreter encounters the exit(), it gives the SystemExit exception. Also, it does not print the stack trace, which means why the error occurred.

Output- Use exit() or Ctrl-Z plus Return to exit

Following is the code for exiting the program if we encounter a voter with age less than 18.

ages=[19,45,12,78] for age in ages: if age < 18: print(age,"not allowed") exit() else: print(age,"allowed")

Output- 19 allowed 45 allowed 12 not allowed

If we run the program in ipython the output is-

2. Python exit using quit()

This function works exactly as the exit(). There is not a single difference. It is to make the language more user-friendly. Just think, you are a newbie to the python language, what function you will think of should be used to exit the program? Exit or quit, right? This is what makes Python an easy to use language. Like the python exit function, the python quit() does not leave any stack trace and should not be used in real life.

Suppose, we want to exit the program when we encounter a name in marks list-

marks=[78,89,92,"ashwini",56] for i in marks: if type(i) != int : print("Oops!! Encountered a non-int value:",i) quit()

Output- Oops!! Encountered a non-int value: ashwini

3. Sys.exit() Function in Python

This function is beneficial and can be used in the real world or production environment because it is a function of the sys module available everywhere. We should use this function for controlling the terminal a=when we have big files.

import sys age = 15 if age < 18: sys.exit("Voting not allowed because the age is less than 18") else: print("Voting allowed")

Output- Voting not allowed because the age is less than 18

4. os._exit Function In Python

This function calls the C function =_exit() which terminates the program immediately. Also, this statement “can never return”.

Difference between exit(0) and exit(1)

The main difference between exit(0) and exit(1) is that exit(0) represents success with any errors and exit(1) represents failure.

Must Read:

Conclusion

The exit function is a useful function when we want to exit from our program without the interpreter reaching the end of the program. Some of the functions used are python exit function, quit(), sys.exit(), os._exit(). We should use these functions according to our needs.

Try to run the programs on your side and let me know if you have any queries.

Happy Coding!

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