[PYTHON] I read PEP 584 (Add Union Operators To dict)

The other day, PEP 584 (Add Union Operators To dict) became Final Commit / python / peps / pull / 1440) I saw it. So, this time I will read PEP 584.

Overview

• I want a nice way to combine two dictionaries
• Since d1.update (d2) rewrites d1, there are occasions when a temporary variable is prepared, and since it is not an expression, it cannot be used as a parameter.
• {** d1, ** d2} is not good
• collections.ChainMap is minor and has the problem of rewriting d1
• dict (d1, ** d2) will result in an error if the key is not a string
• Allow the | operator to be used to combine dictionaries
• Available from Python 3.9

approach

Combine the two dictionaries with d1 | d2. If you have the same key, it will be overwritten with the contents of the dictionary on the right, so it is not commutative (the order of the keys in the new dictionary will also change).

>>> d = {'spam': 1, 'eggs': 2, 'cheese': 3}
>>> e = {'cheese': 'cheddar', 'aardvark': 'Ethel'}
>>> d | e
{'spam': 1, 'eggs': 2, 'cheese': 'cheddar', 'aardvark': 'Ethel'}
>>> e | d
{'aardvark': 'Ethel', 'spam': 1, 'eggs': 2, 'cheese': 3}

It also supports the | = operator.

>>> d |= e
>>> d
{'spam': 1, 'eggs': 2, 'cheese': 'cheddar', 'aardvark': 'Ethel'}

Impressions

• It feels strange, but you should get used to it after a while. maybe…
• d = dict (d1); d.update (d2) has been written many times, so I'm happy
• It's nice to be able to write clearly