Check if string is type

Python normally looks up names using LEGB. Since you have no non-locals, you can ignore E. You know that you don't have a local name, so L is gone too. So the equivalent lookup would indeed be a call to globals and a search of builtins.

You don't need a dictionary if all you care about are the keys. That way, you explicitly pass in simple strings and don't need to play games with extra characters:

import builtins
from inspect import isclass

def convert(target, *names):
    for name in names:
        obj = globals().get(name, getattr(builtins, name, None))
        if isclass(obj):
            return obj(target)
    return converting