unpack nested dicts by concatenating keys

unpack_dict.py

def unpack_dict(d, keys=None, passed=None, filterNone=True):
    """
    Unpack nested dictionary with _ separted keys
    
    :param dict d: nested dictionary to unpack
    :param list keys: sequence of access keys
    :param dict passed: dict to update with flattened keys
    :param bool filterNone: filter out keys where value is None
    :return: flattened dict
    :rtype: dict
    """
    if passed is None:
        passed = {}
    if keys is None:
        keys = []
        
    for key, value in d.iteritems():
        if isinstance(value, dict):
            passed = unpack_dict(value, keys + [key], passed, filterNone)
        elif not filterNone or value is not None:
            passed["_".join(keys + [key])] = value
                
    return passed