checks the response if the server returned an error raises an exception.

def check_response(response):
    """
    checks the response if the server returned an error raises an exception.
    """
    if response.status_code < 200 or response.status_code > 300:
        raise ServerError('API requests returned with error: %s'
                          % response.status_code)

    try:
        response_text = loads(response.text)
    except ValueError:
        raise ServerError('The API did not returned a JSON string.')

    if not response_text:
        raise EmptyResponse()

    if 'failure' in response_text:
        if response_text['failure'] == 'Falscher Dateityp':
            raise UnsupportedFormat('Please look at picflash.org '
                                    'witch formats are supported')
        else:
            raise UnkownError(response_text['failure'])