Python 3.9.0 : Union and in-place union operators

Python introduces two new operators for dictionaries named union used in code with pipe operator | and in-place union used in python code with this |=.

I this tutorial I will show you how can be used:

[mythcat@desk ~]$ python3.9 
Python 3.9.0 (default, Oct  6 2020, 00:00:00) 
[GCC 10.2.1 20200723 (Red Hat 10.2.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> step_one = {"worker_one":"task_one", "worker_two":"task_two"}
>>> step_two = {"worker_three":"task_one", "worker_fouw":"task_two"}
>>> merged_step_one_step_two = {**step_one, **step_two}
>>> empty = {}
>>> empty |= step_one
>>> empty
{'worker_one': 'task_one', 'worker_two': 'task_two'}
>>> step_one 
{'worker_one': 'task_one', 'worker_two': 'task_two'}
>>> step_two
{'worker_three': 'task_one', 'worker_fouw': 'task_two'}
>>> all = step_one | step_two 
>>> all 
{'worker_one': 'task_one', 'worker_two': 'task_two', 'worker_three': 'task_one', 'worker_fouw': 'task_two'} 
>>> copy_step_one = empty | step_one
>>> copy_step_one 
{'worker_one': 'task_one', 'worker_two': 'task_two'} 
>>> copy_step_one |= [("manager", "steps")]
>>> copy_step_one 
{'worker_one': 'task_one', 'worker_two': 'task_two', 'manager': 'steps'}

You can easily see how to use these operators with the dictionaries created and how to add lists to dictionaries. Operations with these operators always result in a dictionary. The order of these operations is important, see example:

>>> numbers = {0: "zero", 1: "one"}
>>> numbers_one = {0: "zero", 1: "one"}
>>> numbers_two = {0: "zero", 2: "two"}
>>> numbers_one | numbers_two
{0: 'zero', 1: 'one', 2: 'two'}
>>> numbers_two | numbers_one
{0: 'zero', 2: 'two', 1: 'one'}
>>> numbers_three = {0: 'zero', 11: 'error 1', 22: 'error 2', 33:'error 3'}
>>> numbers_three | numbers_one
{0: 'zero', 11: 'error 1', 22: 'error 2', 33: 'error 3', 1: 'one'}
>>> numbers_one | numbers_three
{0: 'zero', 1: 'one', 11: 'error 1', 22: 'error 2', 33: 'error 3'}

You can see how the dictionaries are overwritten by the union operation. These operations are implemented through dunder operations for most the dictionary objects except abstract classes. Dunder or magic methods in Python are the methods having two prefix and suffix underscores in the method name. You can find on this page.