Re: [Python-ideas] PEP: Dict addition and subtraction

Fri, 08 Mar 2019 08:24:53 -0800

Hello,

I've just read your PEP 585 draft and have some questions.
When you say
"

Like the merge operator and list concatenation, the difference operator requires both operands to be dicts, while the augmented version allows any iterable of keys.

>>> d - {'spam', 'parrot'}
Traceback (most recent call last):
  ...
TypeError: cannot take the difference of dict and set

>>> d -= {'spam', 'parrot'}
>>> print(d)
{'eggs': 2, 'cheese': 'cheddar'}

>>> d -= [('spam', 999)]
>>> print(d)
{'spam': 999, 'eggs': 2, 'cheese': 'cheddar', 'aardvark': 'Ethel'}
 
"

The option d -= {'spam', 'parrot'} where parrot does not exist in the d dict, will raise an exception (eg. KeyNotFound) or be silent?

The option d -= [('spam', 999)] should remove the pair from the dict, correct? But the print that follows still shows it there. It's a mistake or am I missing something?


Best regards,

João Matos

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