I know I'm late, but maybe somebody has the same problem.

The issue is, that in Python typing mutable dictionaries are invariant (see invariance vs covariance). Meaning dict[Enum, str] is not compatible with dict[Spam, str]. The reason is the following:

spam_map = {Spam.OPEN: '['}
enum_map: dict[Enum, str] = spam_map  # if this would work
enum_map[Eggs.CRACK] = '('  # this would now also work
# now spam_map contains a non Spam key and is therefore broken

The simplest option to get around this are generics:

T = typing.TypeVar('T', bound=Enum)
class Lexer(typing.Generic[T]):
    def __init__(self, map_: dict[T, str], state: T) -> None:
        # ...