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

In this python tutorial, you will learn about the Python exit command with a few examples. Here we will check:

• 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

Python exit command

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.

Example:

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

Example:

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.

Example:

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.

Example:

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.

Example:

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.

Example:

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

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How do you implement ‘EXIT_CODES’ in python?

Initially i thought to do something like:

But than I’ve realized that I’ll have to know exactly the total number of EXIT_CODES, so that I can pass it to the range() function. Let’s suppose I’ll have 87 (arbitrary) EXIT_CODES. I don’t want to count to 87 (not that it’s hard) but I am looking for a more elegant solution.

EDIT: EXIT_CODE is a negative int that will be passed to sys.exit . Instead of writing the number I prefer to use some sort of constants (something like #defines or enums in C, or enums in Java).

5 Answers 5

Sounds like what you want is the Python equivalent of an enumeration in C# or other similar languages. How can I represent an ‘Enum’ in Python? provides several solutions, though they still require the number of items you have. EDIT: How can I represent an ‘Enum’ in Python? looks way better.

Or you could try something like this (probably not the best solution, though):

Maybe I don’t understand the question, but why don’t you simply make a dictionary of exit codes and implement the desired behaviour in a function?

So you can use it like

And if you want to make «automatic» assignment of numbers (I don’t recommend this) you can simply create a list of exit codes and return the negative of the index:

(for the last one, you can implement a function similar to the dictionary-based one)

I must note that it’s not at all certain a negative status makes sense for sys.exit(); at least on Linux, it will be interpreted as an unsigned 8-bit value (range 0-255). As for an enumerated type, it’s possible to do something like:

Resulting in something like:

The predefined values in normal Unix systems are EXIT_FAILURE=1 and EXIT_SUCCESS=0.

Addendum: Considering the concern about IDE identification of identifiers, one could also do something like:

Second edit: Couldn’t keep away. Here’s a variant that assigns the values in the order you’ve written the names.

Obviously the growing complexity is inelegant, but it does work.

Коды выхода в Python

Я получил сообщение, что script xyz.py returned exit code 0 . Что это значит?

Что означают коды выхода в Python? Сколько их там? Какие из них важны?

12 ответов:

то, что вы ищете в скрипте вызовы sys.exit() . Аргумент этого метода возвращается в среду в качестве кода выхода.

вполне вероятно, что скрипт никогда не вызывает метод exit, и что 0-это код выхода по умолчанию.

необязательный аргумент arg может быть целое состояние выхода (по умолчанию ноль), или другой тип объекта. Если это целое число, ноль считается » успешным окончанием» и любое ненулевое значение считается «анормалное прекращение» раковинами и подобный. Большинство систем требуют этого быть в диапазоне 0-127, и производить неопределенные результаты в противном случае. Некоторые системы Конвенции для присвоение конкретных значений конкретные коды выхода, но это как правило, недоразвиты; в Unix программы обычно используют 2 для команды ошибки синтаксиса строки и 1 для всех остальных виды ошибок.

один пример, где коды выхода используются в сценариях оболочки. В bash, вы можете проверить специальную переменную $? для последнего состояния выхода:

лично я стараюсь использовать коды выхода, которые я нахожу в /usr/include/asm-generic/errno.h (на Linux), но я не знаю, если это правильно.

есть errno модуль, который определяет стандартные коды выхода:

например, доступ запрещен код ошибки 13:

для записи можно использовать стандартные коды выхода POSIX defined здесь.

коды выхода 0 обычно означают: «здесь все в порядке.»Однако, если программист сценария не следовал конвенции, вам, возможно, придется проконсультироваться с источником, чтобы увидеть, что это значит. Обычно ненулевое значение возвращается в виде кода ошибки.

команды операционной системы кодов выхода. Ищите коды выхода linux чтобы увидеть некоторые материалы по этому вопросу. Оболочка использует коды выхода, чтобы решить, если программа работала, были проблемы или не удалось. Есть некоторые усилия по созданию стандартных (или, по крайней мере, часто используемых) кодов выхода. Смотрите это Расширенный Скрипт проводки.

Exiting from python Command Line

To exit from Python command line, I have to type exit(). If I type exit, it says

Usually when you type exit , you would want to exit the program. Why does the interpreter give me the above error when it knows I am trying to exit the command line? Why doesn’t it just exit? I know it doesn’t matter and its a silly question but I am curious.

11 Answers 11

In my python interpreter exit is actually a string and not a function — ‘Use Ctrl-D (i.e. EOF) to exit.’ . You can check on your interpreter by entering type(exit)

In active python what is happening is that exit is a function. If you do not call the function it will print out the string representation of the object. This is the default behaviour for any object returned. It’s just that the designers thought people might try to type exit to exit the interpreter, so they made the string representation of the exit function a helpful message. You can check this behaviour by typing str(exit) or even print exit .

This works for me, best way to come out of python prompt.

When you type exit in the command line, it finds the variable with that name and calls __repr__ (or __str__ ) on it. Usually, you’d get a result like:

But they decided to redefine that function for the exit object to display a helpful message instead. Whether or not that’s a stupid behavior or not, is a subjective question, but one possible reason why it doesn’t «just exit» is:

Suppose you’re looking at some code in a debugger, for instance, and one of the objects references the exit function. When the debugger tries to call __repr__ on that object to display that function to you, the program suddenly stops! That would be really unexpected, and the measures to counter that might complicate things further (for instance, even if you limit that behavior to the command line, what if you try to print some object that have exit as an attribute?)

Exit codes in Python

I got a message saying script xyz.py returned exit code 0 . What does this mean?

What do the exit codes in Python mean? How many are there? Which ones are important?

13 Answers 13

You’re looking for calls to sys.exit() in the script. The argument to that method is returned to the environment as the exit code.

It’s fairly likely that the script is never calling the exit method, and that 0 is the default exit code.

From the documentation for sys.exit :

The optional argument arg can be an integer giving the exit status (defaulting to zero), or another type of object. If it is an integer, zero is considered “successful termination” and any nonzero value is considered “abnormal termination” by shells and the like. Most systems require it to be in the range 0-127, and produce undefined results otherwise. Some systems have a convention for assigning specific meanings to specific exit codes, but these are generally underdeveloped; Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors.

One example where exit codes are used are in shell scripts. In Bash you can check the special variable $? for the last exit status:

Personally I try to use the exit codes I find in /usr/include/asm-generic/errno.h (on a Linux system), but I don’t know if this is the right thing to do.

For the record, you can use POSIX standard exit codes defined here.