<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def generate_private_key(key_type):
 """ Generate a random private key using sensible parameters. :param str key_type: The type of key to generate. One of: ``rsa``. """

    if key_type == u'rsa':
        return rsa.generate_private_key(
            public_exponent=65537, key_size=2048, backend=default_backend())
    raise ValueError(key_type)