Hashtable/dictionary/map lookup with regular expressions

Question

I\'m trying to figure out if there\'s a reasonably efficient way to perform a lookup in a dictionary (or a hash, or a map, or whatever your favorite language calls it) where the

Answer 1

I don't think it's even theoretically possible. What happens if someone passes in a string that matches more than 1 regular expression.

For example, what would happen if someone did:

>>> regex_dict['FileNfoo']

How can something like that possibly be O(1)?