def get_pools(time_span=None, api_code=None):
    """Get number of blocks mined by each pool.

    :param str time_span: duration of the chart.
    Default is 4days (optional)
    :param str api_code: Blockchain.info API code (optional)
    :return: an instance of dict:{str,int}
    """

    resource = 'pools'
    if time_span is not None:
        resource += '?timespan=' + time_span
    if api_code is not None:
        resource += '&api_code=' + api_code
    response = util.call_api(resource, base_url='https://api.blockchain.info/')
    json_response = json.loads(response)
    return {k: v for (k, v) in json_response.items()}
Get number of blocks mined by each pool.

    :param str time_span: duration of the chart.
    Default is 4days (optional)
    :param str api_code: Blockchain.info API code (optional)
    :return: an instance of dict:{str,int}