On 1/11/21 1:16 PM, Larry Hastings wrote:
On 1/11/21 12:32 PM, Paul Bryan wrote:
*1. Backwards Compatibility*
PEP 563 <https://www.python.org/dev/peps/pep-0563> changed the
semantics of annotations. When its semantics are active, annotations
must assume they will be evaluated in /module-level/ scope. They may
no longer refer directly to local variables or class attributes.
Given get_type_hints can be provided localns argument, this statement
is not exactly true.
PEP 563 states:
For code that uses type hints, the typing.get_type_hints(obj,
globalns=None, localns=None) function correctly evaluates
expressions back from its string form.
So, if you are passing in a localns argument that isn't None, okay,
but you're not using them "correctly" according to the language.
Also, this usage won't be compatible with static type checkers.
Whoops! Let me walk that back a little. I'd been assuming that PEP 563
used the terms "annotations" and "type hints" to mean the exact same
thing. But careful reading of PEP 484 suggests that they're distinct
concepts; all "type hints" are annotations, but not all annotations are
"type hints".
So: if you're using annotations for something besides "type hints", such
that you have a use for a non-None localns, I guess you have two options
with my PEP: either
a) use strings for your annotations where you need localns to work for
you, or
b) skip using annotations syntax and instead write your own custom
__co_annotations__ function. Or, you could mix and match, using
annotations syntax where it was convenient, and overriding only the
troublesome spots in your custom __co_annotations__ function:
def foo(a:int=3, b):
...
foo_static_annotations = foo.__annotations__
def foo_dynamic_closure_annotations():
annotations = dict(foo_static_annotations)
annotations['b'] = MyExcitingLocallyDefinedClosureTypeThing
return annotations
foo.__co_annotations = foo_dynamic_closure_annotations
Cheers,
//arry/
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