<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def create_key(file_):
 """ Create a key and save it into ``file_``. Note that ``file`` must be opened in binary mode. """

    pkey = crypto.PKey()
    pkey.generate_key(crypto.TYPE_RSA, 2048)

    file_.write(crypto.dump_privatekey(crypto.FILETYPE_PEM, pkey))
    file_.flush()