except handler type error should admit the possibility of tuples

[benjaminp]

$ mypy --version
mypy 0.610
$ cat exception.py
def f() -> None:
    excs = [IOError, LookupError]
    try:
        pass
    except excs:
        pass
$ mypy exception.py 
exception.py:5: error: Exception type must be derived from BaseException

While it's true that this code is incorrect, I probably want to fix it by writing excs = (IOError, LookupError) rather than somehow making my list a subclass of BaseException.

[JukkaL]

The error message is confusing in this case -- mypy accepts tuples already. One way to fix this would be to check if the exception is not a type object, and in that case change the message to something like this:

exception.py:5: error: Exception type must be a class derived from BaseException (or a tuple of exception classes)

[bhrutledge]

I was able to avoid this error by making excs a tuple, instead of a list:

def f() -> None:
    excs = (IOError, LookupError)
    try:
        pass
    except excs:
        pass