def load(account_id):
"""
Return the account object associated to *account_id* loaded from
existing configuration. If the *account_id* does not correspond to a
valid account it returns a
:class:`libturpial.exceptions.ErrorLoadingAccount` exception.
If credentials in configuration file are empty it returns a
:class:`libturpial.exceptions.EmptyOAuthCredentials` exception.
"""
if not AccountConfig.exists(account_id):
raise ErrorLoadingAccount("Account has no stored credentials")
username = get_username_from(account_id)
protocol_id = get_protocol_from(account_id)
account = Account.new(protocol_id, username)
account.config = AccountConfig(account_id)
key, secret = account.config.load_oauth_credentials()
account.setup_user_credentials(account.id_, key, secret)
account.fetch()
return account
