`ChildProcessError`

ChildProcessError is a built-in exception that is raised when an operation on a child process fails.

This exception is part of the OSError family and typically occurs when an error arises in handling a child process. For example, you might encounter this exception when trying to interact with a process that has already terminated or when a process-related operation isn’t permitted.

`ChildProcessError` Occurs When

Attempting to terminate a child process that has already exited
Trying to communicate with a child process using pipes after the process has finished

`ChildProcessError` Can Be Used When

You should handle the exception in subprocess management scenarios to ensure robustness in code that deals with multiple processes.

`ChildProcessError` Examples

An example of when the exception appears:

Python
      
        
      
    
>>> import os
>>> os.wait()
Traceback (most recent call last):
  ...
ChildProcessError: [Errno 10] No child processes

An example of how to handle the exception in a subprocess management scenario on a UNIX system:

Pythonchildprocess.py
      
    
import subprocess
import os

process = subprocess.Popen(["sleep", "0.1"])
process.wait()

try:
    os.wait()
except ChildProcessError as e:
    print("Handled ChildProcessError:", e)

In this code example, you start a subprocess that runs briefly, calling the UNIX command-line utility sleep in line 4. Then, you wait for it to finish in line 5.

Later in your code, you might again try to wait for a child process, which is exemplified with calling os.wait() again in line 8 inside the try block. Since the child process has already terminated, os.wait() may raise a ChildProcessError. To avoid that, you catch the exception in the except block.

The subprocess Module: Wrapping Program With Python

Tutorial

The subprocess Module: Wrapping Programs With Python

In this tutorial, you'll learn how to leverage other apps and programs that aren't Python, wrapping them or launching them from your Python scripts using the subprocess module. You'll learn about processes all the way up to interacting with a process as it executes.

intermediate

For additional information on related topics, take a look at the following resources: