multiprocessing (Python 2.4/2.5 Backport)

Common errors

• ImportError: No module named multiprocessing

  cause The `multiprocessing` backport package is not installed in your Python 2.4/2.5 environment.
  fix Run `pip install multiprocessing` in your Python 2.4/2.5 environment to install the backport.

• SyntaxError: Missing parentheses in call to 'print'

  cause You are attempting to run Python 2.x code (using `print` as a statement) with a Python 3 interpreter.
  fix Ensure you are running the code with a Python 2 interpreter. If migrating to Python 3, convert `print` statements to `print()` functions.

• RuntimeError: An attempt has been made to start a new process before the current process has finished its bootstrapping phase.

  cause The `multiprocessing` module (both backport and standard library) requires the entry point of the script to be protected by an `if __name__ == '__main__':` block, especially on Windows.
  fix Ensure all code that creates child processes is encapsulated within an `if __name__ == '__main__':` block in your main script.

• PicklingError: Can't pickle <type 'function'>: attribute lookup __builtin__.function failed

  cause Objects (especially functions defined locally or complex custom objects) passed between processes must be picklable, but an unpicklable object was used.
  fix import multiprocessing # Define functions at the module level def my_picklable_function(data): return data * 2 if __name__ == '__main__': p = multiprocessing.Process(target=my_picklable_function, args=(5,)) p.start() p.join()

• AttributeError: 'module' object has no attribute 'cpu_count'

  cause The `multiprocessing.cpu_count()` function was introduced in Python 2.6 (and the standard library `multiprocessing`) and is not available in the Python 2.4/2.5 backport.
  fix import os import multiprocessing def get_cpu_count_manual(): if os.name == 'posix': try: return os.sysconf('SC_NPROCESSORS_ONLN') except (AttributeError, ValueError): pass return 1 # Fallback if specific method fails or for other OS num_cpus = get_cpu_count_manual() print('Detected CPUs:', num_cpus)

Warnings

• breaking This PyPI package is a backport for Python 2.4/2.5 and is not compatible with Python 3.x. Attempting to use it will lead to syntax errors or unexpected behavior.
  Fix: For Python 3.x, use the built-in `multiprocessing` module directly without `pip install multiprocessing`.
• gotcha Installing `multiprocessing` via pip in Python 2.6+, 2.7, or Python 3.x environments will result in an old, incompatible version being installed. This can cause conflicts with the standard library module or lead to confusion.
  Fix: Do not install this package on Python 2.6+ or Python 3.x. The functionality is built into the standard library.
• deprecated This package is a backport for Python 2.4/2.5, both of which are long past their end-of-life. The package is considered abandoned and should not be used for new development. Critical security vulnerabilities or bugs will not be addressed.
  Fix: Upgrade to a modern, supported Python version (Python 3.x) and utilize its built-in `multiprocessing` module.

Install

• pip install multiprocessing For Python 2.4/2.5 only

Imports

• Process

  from multiprocessing import Process

  This import path is consistent with the standard library version but applies to the backport.

Quickstart

A basic example demonstrating how to create and run a process using the backported `multiprocessing` module. This code is written for Python 2.x syntax.

# For Python 2.4/2.5 using the multiprocessing backport
import multiprocessing
import os

def worker_function(name):
    print "Worker %s: PID %s" % (name, os.getpid())
    return

if __name__ == '__main__':
    # The 'if __name__ == '__main__':` guard is crucial, especially on Windows.
    process = multiprocessing.Process(target=worker_function, args=('Alice',))
    process.start()
    process.join()
    print "Main process: PID %s" % os.getpid()