The introduction of the Python multiprocessing documentation (https://docs.python.org/2.7/library/multiprocessing.html#introduction) clearly mentions that all the functionality within this package requires the main module to be importable to the children (https://docs.python.org/3.3/library/multiprocessing.html).

The __main__ module is not importable to the children in IDLE, even if you run the script as a file with IDLE. To get the correct result, we will run all the examples from Command Prompt:

> python multiprocessing_example.py

Here, multiprocessing_example.py is the script's name.