mypy interprets variable as a type during Enum indexing

[cduong]

Example code, where row.status is expected to be a string:

class Status(Enum):
    SUCCEEDED = 1
    FAILED = 2

def get_status(row):
    # type: (Any) -> Status
    status = Status[row.status]
    return status

Error:

note: In function "test":
error: Invalid type "row"

In a similar case, I also received this error in addition to the above: error: Generic type not valid as an expression any more (use '# type:' comment instead)

[gvanrossum]

PEP 435 enums allow indexing the class to dynamically look up an enum. E.g. `Color['green']` is the same as`Color.green`. If the class is not generic mypy shouldn't flag it as an error.

[Stiivi]

Different kind of error is reported when more complex indexing argument is passed:

class Choice(Enum):           
    foo = 0                   
    bar = 1                   
                              
def from_value(value: str) -> Choice: 
    return Choice[value.lower()] 

Error: Type expected within [...]

[gvanrossum]

I think maybe this also ought to be given higher priority.

[gvanrossum]

FWIW I am going special-case enums here, rather than change the behavior for all non-generic classes. (Generic enums make no sense, but we don't currently detect this.)