def begin_transaction(self):
conn = self.get_conn()<EOL>resp = (conn<EOL>.projects()<EOL>.beginTransaction(projectId=self.project_id, body={})<EOL>.execute(num_retries=self.num_retries))<EOL>return resp['<STR_LIT>']<EOL>
Begins a new transaction.

.. seealso::
    https://cloud.google.com/datastore/docs/reference/rest/v1/projects/beginTransaction

:return: a transaction handle.
:rtype: str