Python exit if no arguments

Complete python exit tutorial with examples in 2023

Python provides many exit functions using which a user can exit the python program. In this blog, we will learn everything about the python exit function. So let’s get started.

Types of python exit function

Python mainly provides four commands using which you can exit from the program and stop the script execution at a certain time. The 4 types of exit commands are:-

Python exit() function

The python exit() function is available in the site module. It is used for the exit or termination of a Python script. The exit command should not be used in production and can only be used for interpreters. Below is the sample python code with the exit function.

This gives the below output:

You can also use exit() with an argument which is the exit code, for example:

Python exit(0)

In Python, the exit(0) function is used to exit or terminate a Python script and return an exit code of 0. The exit code 0 is a standard convention to indicate that the program has terminated without errors. Below is the sample python code for exit(0)

Please note that you can also use exit() with no arguments, which is equivalent to calling sys.exit(0)

Python exit(1)

In Python, the exit(1) function is used to exit or terminate a Python script and return an exit code of 1. Exit code 1 indicates an unsuccessful termination or an error occurred during the execution of the script. Below is the sample python code for exit(1)

age = 45 if age < 50: # exit the program print(exit) exit(1)

Please note that the exit code of 1 is just a convention and you can use any other integer value to indicate different types of errors.

Python quit() function

In Python, the quit() function is equivalent to the exit() function. However, the quit() function is only available n python2 but not in python 3.Quit() function should only be used in the interpreter. Below is the sample python code which uses the quit() function.

age = 45 if age < 50: # quit the program print(quit) quit()

The above code defines a variable age as 45 and then checks if the value of age is less than 50. If it is, it will print the value of the quit function and then call the quit() function to stop the program from running.

Python sys.exit() function

In Python, the sys.exit() function is used to exit or terminate a Python script. The sys.exit() function can be used in production because it raises an SystemExit exception that causes the interpreter to exit. You can use the sys.exit() program with or without arguments. With an argument, the program will exit and return a successful exit code on 0, whereas with an argument, which is the exit code like:

import sys for i in range(1,5): print(i) if i == 3: sys.exit()

The above code will print the numbers from 1 to 3, and then the sys.exit() function will be called when the value of i is 3. This will cause the script to terminate and end the program with an exit code of 0, indicating a successful termination.

python os._exit() function

In Python, the os._exit() function is used to immediately exit the current process without performing any cleanup or finalization tasks. The os._exit() does not call any cleanup handlers, close open files, or flush stdio buffers. This can make it more efficient for exiting a program, but it also means that any necessary cleanup or finalization tasks will not be executed. It is important to consider the use of os._exit() as it may leave resources open and could cause issues when running in a multi-threaded environment.

Below is the sample python code using the os._exit() function

import os for i in range(1,5): print(i) if i == 3: os._exit(0)

After the number 3 is printed, the os._exit(0) function will be called, causing the script to immediately terminate and exit the process without printing the remaining numbers (4) in the range.

Python exit vs quit

In Python, the exit() function and quit() function are used to terminate a Python script. Both these functions raise a SystemExit exception, which causes any finally clauses in a try/finally statements to be executed and any unhandled exceptions to be logged.

exit() is a built-in function in both Python2 and Python3, while quit() is a built-in function only in Python2. In Python3 and it is recommended to use exit() or sys.exit() instead.

It’s important to ensure that any resources which the program uses, like file handlers, sockets, or database connections, are closed correctly before exiting the program using exit() or quit() with a non-zero exit code.

Python exit with an error

In Python, you can use the sys.exit() function with a non-zero exit code to exit the program and indicate that an error has occurred. For example:

import sys for i in range(1,5): if i == 3: sys.exit("Exiting,as number is equal to 3 ") print(i)

In the above code, the script will print the numbers from 1 to 2 and then exit the program when the value of i is 3. The sys.exit() function will be called, which will cause the script to terminate and end the program with an exit code of 0, indicating a successful termination. The message “Exiting, as number is equal to 3” will also be printed before the script exits.

Python exit from a program gracefully

Exiting a program gracefully refers to allowing the program to perform any necessary cleanup or finalization tasks before terminating. In Python, you can exit a program gracefully by using the sys.exit() function along with finally block to handle any necessary cleanup or finalization tasks.

For example, Below is the sample try-finally block to perform cleanup tasks before exiting the program:

def test(): try: # code to run finally: # cleanup tasks print("Cleanup Done") sys.exit(0) if __name__ == "__main__": test()

Conclusion

I hope you have liked this tutorial on the python exit function. Please do let me know if you need further inputs.

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Exit a Process with sys.exit() in Python

You can call sys.exit() to exit a process.

In this tutorial you will discover how to use sys.exit() with parent and child processes in Python.

What is sys.exit()

The sys.exit() function is described as exiting the Python interpreter.

Raise a SystemExit exception, signaling an intention to exit the interpreter.

— sys — System-specific parameters and functions

When called, the sys.exit() function will raise a SystemExit exception.

This exception is (typically) not caught and bubbles up to the top of a stack of the running thread, causing it and the process to exit.

… This allows the exception to properly propagate up and cause the interpreter to exit. When it is not handled, the Python interpreter exits; no stack traceback is printed.

— Built-in Exceptions

The sys.exit() function takes an argument that indicates the success or failure of the exit status.

A value of None (the default) or zero indicates a successful , whereas a larger value indicates an unsuccessful exit.

If the value is an integer, it specifies the system exit status (passed to C’s exit() function); if it is None, the exit status is zero; if it has another type (such as a string), the object’s value is printed and the exit status is one.

— Built-in Exceptions

Importantly, finally operations in try-except-finally and try-finally patterns are executed. This allows a program to clean-up before exiting.

Cleanup actions specified by finally clauses of try statements are honored …

— sys — System-specific parameters and functions

In multiprocessing programming, we may make calls to sys.exit() to close our program.

How does sys.exit() interact with the main process and child processes in Python?

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sys.exit() and Exit Codes

Each Python process has an exit code.

The process exitcode is set automatically, for example:

• If the process is still running, the exitcode will be None.
• If the process exited normally, the exitcode will be 0.
• If the process terminated with an uncaught exception, the exitcode will be 1.

The exitcode can also be set via a call to sys.exit().

For example, a child process may exit with a call to sys.exit() with no arguments.

The child process will terminate and the exitcode will be set to 0.

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How to Use sys.exit()

The sys.exit() function is used by simply making the function call.

A normal exit can be achieved by calling the function with no argument, e.g. defaulting to a value of None.

A normal exit can also be achieved by passing the value of None or 0 as an argument.

An unsuccessful exit can be signaled by passing a value other than 0 or None.

This may be an integer exit code, such as 1.

Alternatively, it may be a string value that may be reported as part of the exit.

Now that we know how to use sys.exit(), let’s look at some worked examples.

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Exit the Main Process

We can explore how to exit the main process using sys.exit().

In this example we will report a message, block for a moment, then exit successfully. We will also include code after the call to sys.exit() to demonstrate that indeed the program is terminated and additional code is unreachable.

The complete example is listed below.

Running the example first reports a message that the main process is running.

The process then blocks for two seconds.

Once awake, the process reports a message then calls sys.exit() to exit normally. The program terminates and the final print statement is never reached.

When the sys.exit() function is called, a SystemExit exception is raised in the main thread. The main thread terminates. As there are no other threads and no child processes, the main process terminates.

Next, let’s explore calling sys.exit() from a child process.

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Exit a Child Process

We can explore calling sys.exit() from a child process.

In this example we will execute a new function in a child process. The child process will report a message, block for a moment, then call exit with a value of one to indicate an unsuccessful exit. It will also include code after the call to exit to confirm that additional code is not reachable. The main process will report the status and exitcode of the child process.

First, we can define a function to execute in a child process.

The function reports a message, blocks, then exits with an exit code of one.

The task() function below implements this.

Next, in the main process we can create a new multiprocessing.Process instance and configure it to execute our task() function.

We can then start the process and wait for it to terminate.

Finally, we can check the running status of the child process to confirm it has terminated and report the exitcode.

Tying this together, the complete example is listed below.

Running the example first creates a child process configured to execute our target function.

The main process then starts the child process then blocks until it terminates.

The child process first reports a message that it is running then sleeps for two seconds. It then awakes, reports a message and calls sys.exit() with an exitcode of 1.

The child process terminates and the main process wakes up.

The status of the child process is reported indicating that it is no longer running (as expected) and that the exit code was 1, as we set when we called sys.exit().

This highlights how a child process may terminate itself and how the parent process may check the exitcode of a child process.

Exit the Main Process With a Child Process

Calling sys.exit() in a parent process will not terminate the process if it has one or more running child processes.

We can explore this with a worked example.

In this example, we will first start a child process and have it block for a moment then check the running status and exit code of the parent process. The parent process will start the child process, block for a moment then attempt to terminate with a call to sys.exit(). The child process will continue running and will show that indeed the parent process is still alive, even after its call to sys.exit().

First, we can define a target task function.

The function will first report a message to indicate that it is running. It will then block for a few seconds to give time for the parent process to “exit“. It will then wake-up and get access to the multiprocessing.Process instance for the parent process via the multiprocessing.parent_process() function. Finally, the running status and exitcode of the parent process will be reported.

The task() function below implements this.

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