Accessing Python dict values with the key start characters

Question

I was wondering: would it be possible to access dict values with uncomplete keys (as long as there are not more than one entry for a given string)? For example:

Answer 1

Sure it is possible:

print next(val for key, val in my_dict.iteritems() if key.startswith('Date'))

but this incurs a full scan through the dictionary. It only finds the first such matching key (where 'first' is arbitrary) and raises StopIteration instead of KeyError if no keys match.

To get closer to what you are thinking of, it's better to write this as a function:

def value_by_key_prefix(d, partial):
    matches = [val for key, val in d.iteritems() if key.startswith(partial)]
    if not matches:
        raise KeyError(partial)
    if len(matches) > 1:
        raise ValueError('{} matches more than one key'.format(partial))
    return matches[0]