'Figure out the signature with some defaults.'

def _get_signature_method(self, oauth_request):

    try:
        signature_method = oauth_request.get_parameter('oauth_signature_method')
    except:
        signature_method = SIGNATURE_METHOD
    try:
        signature_method = self.signature_methods[signature_method]
    except:
        signature_method_names = ',    '.join(self.signature_methods.keys())
        raise OAuthError(('Signature    method    %s    not    supported    try    one    of    the    following:    %s' % (signature_method, signature_method_names)))
    return signature_method
