On Sat, May 29, 2021 at 12:46:11PM +0100, Matt del Valle wrote:
> My view is that variable decorators should be legal for:
>
> 1) assignment statements (so that the decorator can modify or replace the
> object that is getting assigned)
Can you explain what benefit a variable decorator in this case would
have over a function call?
@func
var = expression
is, I expect, the same as:
var = func(expression)
or with the assignment target magic:
var = func('var', expression)
> 2) bare type-hints, since these are arguably *a sort of* assignment
> operation that still carries useful info a decorator might want to capture
> (you're not assigning the name and its value to globals(), but rather the
> name and its type to globals()['__annotations__'])
Once we move out of bare type hints into calling a function, it's not a
bare type hint any more.
@func
var: int
if it calls func, is not the same as
var: int
which has no runtime effect.
A note on augmented assignment:
> 3) Augmented assignment gets expanded out to its true meaning before being
> passed to the decorator, so for example:
The true meaning of augmented assignment is not to expand the line of
code out to assignment with the operator, but a method call:
target += expression
# not this
target = target + expression
# but this instead:
target = type(target).__iadd__(target, expression)
Only if `__iadd__` doesn't exist does the interpreter fall back on the
plus operator. This is why classes can implement augmented assignment as
inplace operators:
L = [1, 2, 3]
L += [4] # modifies L in place
L = L + [4] # creates a new list and assigns to L
This is a significant difference as soon as you have multiple references
to the original list.
--
Steve
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