'Generates a key_name to be used in creating the underlying object.
The default implementation returns None.
This method can be overridden to control the key generation for
uploaded entities. The value returned should be None (to use a
server generated numeric key), or a string which neither starts
with a digit nor has the form __*__ (see
https://developers.google.com/appengine/docs/python/datastore/entities),
or a datastore.Key instance.
If you generate your own string keys, keep in mind:
1. The key name for each entity must be unique.
2. If an entity of the same kind and key already exists in the
datastore, it will be overwritten.
Args:
i: Number corresponding to this object (assume it\'s run in a loop,
this is your current count.
values: list/tuple of str.
Returns:
A string to be used as the key_name for an entity.'

def generate_key(self, i, values):

    return None
