Dan Snider <mr.assume.a...@gmail.com> added the comment:
It's working as intended. locals() and vars() simply returns the current
frame's f_locals. In functions, modifying this usually accomplishes nothing
useful because the code object has OPTIMIZED and NEWLOCALS flags set, meaning
local variables are looked up or set via the LOAD_FAST and STORE_FAST opcodes
(respectively) which doesn't even look in the f_locals mapping. In this case,
vars() and locals() will build a new dict[*] and fill it with the frame's
fastlocals and unpack any closure cells into it.
The code object used for class bodies however is special and actually *does*
use the mapping in f_locals, which for for classes ultimately built by
builtins.__build_class__ (aka classes built with a `class` statement) will be
whatever the metaclass's __prepare__ returns, which in the case of enums is an
enum._EnumDict instance.
So that's why metaclasses are so powerful. You don't even need to use a
dictionary subclass as the class namespace, since the STORE_NAME opcode will
use PyObject_SetItem; however type.__new__ will make you cast it to a dict, and
even the dict that is wrapped by a MappingProxy after the class has been
created will be a copy anyway.
So anyway, there's nothing actually wrong with the current behavior.
dict.update never calls `self.__getitem__`, and since `_EnumDict.__setitem__`
is where all of the magic happens regular dict.update won't trigger it. I agree
though that adding an update method would be nice though and can be done in
just a few lines of code.
import enum
import sys
def local_update(it=(), **kws):
self = sys._getframe(1).f_locals
d = dict(it, **kws)
for k, v in d.items():
self[k] = v
class MyEnum(enum.Enum):
local_update(a=1, b=2)
assert MyEnum.a.value == 1
[*] it doesn't actually build a new one every time but the only practical
purpose with the NEWLOCALS code.co_code flag set is for introspection with
vars(), locals(), and sys._getframe
----------
nosy: +bup
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue34750>
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