How to Get the Process PID in Python

June 13, 2022 Python Multiprocessing

You can get the process pid via the multiprocessing.Process.pid attribute or via the os.getpid() and os.getppid() functions.

In this tutorial you will discover how to get the process pid in Python.

Let's get started.

Need To Get a Process PID

A process is a running instance of a computer program.

Every Python program is executed in a Process, which is a new instance of the Python interpreter. This process has the name MainProcess and has one thread used to execute the program instructions called the MainThread. Both processes and threads are created and managed by the underlying operating system.

Sometimes we may need to create new child processes in our program in order to execute code concurrently.

Python provides the ability to create and manage new processes via the multiprocessing.Process class.

You can learn more about multiprocessing in the tutorial:

Multiprocessing in Python: The Complete Guide

In multiprocessing, we may need to get the process identifier or PID of a process.

For example:

We may need the pid of the current process.
We may need the pid of a child process.
We may need the pid of the parent process.

How can we get the pid of a process in Python?

What is a PID

PID is an acronym for Process ID or Process identifier.

A process identifier is a unique number assigned to a process by the underlying operating system.

Each time a process is started, it is assigned a unique positive integer identifier and the identifier may be different each time the process is started.

The pid uniquely identifies one process among all active processes running on the system, managed by the operating system.

As such, the pid can be used to interact with a process, e.g. to send a signal to the process to interrupt or kill a process.

How to Get a Process PID

We can get the pid from the multiprocessing.Process instance or via os module functions such as os.getpid() and os.getppid().

Let's take a closer look at each approach in turn.

PID via Process Instance

We can get the pid of a process via its multiprocessing.Process instance.

When we create a child process, we may hang on to the process instance.

Alternatively, we may get the process instance for the parent process via the multiprocessing.parent_process() function or for child process via the multiprocessing.active_children() function.

We may also get the process instance for the current process via the multiprocessing.current_process() function.

For example:

...
# get the process instance
process = multiprocessing.current_process()

Once we have the process instance, we get the pid via the multiprocessing.Process.pid attribute.

For example:

...
# get the pid
pid = process.pid

PID via Module Functions

We can get the pid for the current process via the os.getpid() function.

For example:

...
# get the pid for the current process
pid = os.getpid()

We may also get the pid for the parent process via the os.getppid() function.

For example:

...
# get the pid for the parent process
pid = os.getppid()

Now that we know how to get the pid, let's look at some worked examples.

Get Current Process PID

We can get the pid for the current process via the os.getpid() function.

...
# get the pid
pid = getpid()

The complete example is listed below.

# SuperFastPython.com
# example of getting the pid of the current process
from os import getpid
# get the pid
pid = getpid()
# report the pid
print(pid)

Running the example gets and reports the pid for the current process.

Note, the pid will differ each time the example is run.

Get Current Process PID via the Process Instance

We can get the pid for the current process via the Process instance.

This can be achieved by first getting the multiprocessing.Process instance for the current process.

...
# get the current process instance
process = current_process()

We can then access the pid attribute.

...
# get the pid
pid = process.pid

The complete example is listed below.

# SuperFastPython.com
# example of getting the pid of the current process process instance
from multiprocessing import current_process
# get the current process instance
process = current_process()
# get the pid
pid = process.pid
# report the pid
print(pid)

Running the example gets the process instance for the current process, then reports the pid.

Note, the pid will differ each time the example is run.

Get Parent Process PID

We can get the pid of the parent process via the os.getppid() function.

In this example we can run a custom function in a new child process. The child process will report the pid of the parent process.

First, we need to define a function to run in the child process.

The function will get the pid of the parent process and report it directly.

The task() function below implements this.

# function executed in the child process
def task():
    # get the parent process pid
    pid = getppid()
    # report the pid
    print(pid)

The main process will configure a new multiprocessing.Process instance to execute our custom function, start the process, then wait for the child process to terminate.

...
# configure the child process
child = Process(target=task)
# start the child process
child.start()
# wait for the child process to finish
child.join()

Tying this together, the complete example is listed below.

# SuperFastPython.com
# example of getting the pid of the parent process
from multiprocessing import Process
from os import getppid

# function executed in the child process
def task():
    # get the parent process pid
    pid = getppid()
    # report the pid
    print(pid)

# protect the entry point
if __name__ == '__main__':
    # configure the child process
    child = Process(target=task)
    # start the child process
    child.start()
    # wait for the child process to finish
    child.join()

Running the example configures and starts the child process.

The child process runs, gets the pid of the parent process and reports the value.

Note, the pid will differ each time the example is run.

Get Parent Process PID via the Process Instance

We can get the pid of the parent process via the multiprocessing.Process instance.

In this example we can run a custom function in a new child process. The child process will get the process instance for the parent process, then get the pid from the process instance and report its value.

First, we need to define a function to run in the child process.

The function will first get the multiprocessing.Process instance for the parent process via the multiprocessing.parent_process() function. It will then get the pid from the process instance and report the value.

The task() function below implements this.

# function executed in the child process
def task():
    # get the parent process
    parent = parent_process()
    # get the parent process pid
    pid = parent.pid
    # report the pid
    print(pid)

The main process will configure a new multiprocessing.Process instance to execute our custom function, start the process, then wait for the child process to terminate.

...
# configure the child process
child = Process(target=task)
# start the child process
child.start()
# wait for the child process to finish
child.join()

Tying this together, the complete example is listed below.

# SuperFastPython.com
# example of getting the pid of the parent process via process instance
from multiprocessing import Process
from multiprocessing import parent_process

# function executed in the child process
def task():
    # get the parent process
    parent = parent_process()
    # get the parent process pid
    pid = parent.pid
    # report the pid
    print(pid)

# protect the entry point
if __name__ == '__main__':
    # configure the child process
    child = Process(target=task)
    # start the child process
    child.start()
    # wait for the child process to finish
    child.join()

Running the example configures and starts the child process.

The child process runs, gets the parent process instance, then gets the pid of the parent process and reports the value.

Note, the pid will differ each time the example is run.

Get Child Process PID

We can get the pid of an active child process via the multiprocessing.Process instance.

In this example we will start a child process that executes a custom function. The parent process will then report the pid of the child process directly via the process instance.

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

The function will block for a few seconds, giving the main process enough time to report the process pid.

The task() function below implements this.

# function executed in the child process
def task():
    sleep(2)

Next, the main process will configure and start a new child process to execute the custom function.

...
# configure the child process
child = Process(target=task)
# start the child process
child.start()

The main process will then get the pid of the child process via the multiprocessing.Process instance directly, then report the value.

...
# get the pid of the child process
pid = child.pid
# report the pid
print(pid)

Finally, the main process will wait for the child process to terminate.

...
# wait for the child process to finish
child.join()

Tying this together, the complete example is listed below.

# SuperFastPython.com
# example of getting the pid of a child process
from time import sleep
from multiprocessing import Process

# function executed in the child process
def task():
    sleep(2)

# protect the entry point
if __name__ == '__main__':
    # configure the child process
    child = Process(target=task)
    # start the child process
    child.start()
    # get the pid of the child process
    pid = child.pid
    # report the pid
    print(pid)
    # wait for the child process to finish
    child.join()

Running the example configures and starts the child process.

The child process runs and blocks for a few seconds.

The main process then gets the pid of the child process and reports its value. It then blocks until the child process finishes.

Note, the pid will differ each time the example is run.

Takeaways

You now know how to get the process pid in Python.

If you enjoyed this tutorial, you will love my book: Python Multiprocessing Jump-Start. It covers everything you need to master the topic with hands-on examples and clear explanations.