Type checking breaks on Enum private name mangling

[NoahS2003]

Type: Bug

According to the enum library docs, since Python 3.11 any attribute in an Enum with a private/mangled name will not be converted into an Enum object but will be left as an attribute. In my Python 3.12.2 interpreter, this works as expected. However, Pylance still thinks that its type will be Literal. An example where this happens looks like this:

class MyEnum(enum.Enum):
    A = 1
    B = 2
    C = 3

    __my_dict = {MyEnum.A: "ham", MyEnum.B: "spam", MyEnum.C: "egg"}

    def find_str(self):
        return self.__my_dict.get(self) # Incorrect type hint error on this line

The error produced is as follows:

Cannot access member "get" for type "Literal[MyEnum.__my_dict]"
  Member "get" is unknown

Extension version: 2024.4.1
VS Code version: Code 1.87.2 (Universal) (863d2581ecda6849923a2118d93a088b0745d9d6, 2024-03-08T15:21:31.043Z)
OS version: Darwin arm64 23.4.0
Modes:

System Info

Item	Value
CPUs	Apple M1 (8 x 24)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled
Load (avg)	3, 4, 4
Memory (System)	16.00GB (0.05GB free)
Process Argv	--crash-reporter-id 1123edd3-4687-46ae-9d32-7507d446c5a6
Screen Reader	no
VM	0%

A/B Experiments

vsliv368:30146709
vspor879:30202332
vspor708:30202333
vspor363:30204092
vscorecescf:30445987
vscod805:30301674
binariesv615:30325510
vsaa593:30376534
py29gd2263:30899288
c4g48928:30535728
azure-dev_surveyone:30548225
962ge761:30959799
pythongtdpath:30769146
welcomedialogc:30910334
pythonidxpt:30866567
pythonnoceb:30805159
asynctok:30898717
pythontestfixt:30902429
pythonregdiag2:30936856
pyreplss1:30897532
pythonmypyd1:30879173
pythoncet0:30885854
h48ei257:31000450
pythontbext0:30879054
accentitlementsc:30995553
dsvsc016:30899300
dsvsc017:30899301
dsvsc018:30899302
cppperfnew:31000557
d34g3935:30971562
fegfb526:30981948
bg6jg535:30979843
ccp2r3:30993541
dsvsc020:30976470
pythonait:31006305
jchc7451:30973076
gee8j676:31009558
dsvsc021:30996838
gd77d436:30999572

[erictraut]

Could someone from the pylance team please transfer this to the pyright project?

[erictraut]

Thanks for the issue. I wasn't aware that private attributes were exempt. The EnumMeta metaclass seems to accumulate more and more special cases every release.

I've updated pyright's logic to reflect the runtime behavior. I've also updated the draft chapter that I recently wrote for the Python typing spec on enum type checking so it also reflects this behavior.

Interestingly, mypy also has the same bug. I've filed a bug report here.

[erictraut]

This is addressed in pyright 1.1.358, which I just published.