<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _unhash(hashed, alphabet):
 """Restores a number tuple from hashed using the given `alphabet` index."""

    number = 0
    len_alphabet = len(alphabet)
    for character in hashed:
        position = alphabet.index(character)
        number *= len_alphabet
        number += position
    return number