from itertools import groupby

def dlist_sum_group(
    target_dlist,
    groupby_field_list = [],
    sum_field_list = [],
    field_list = [],
    convert = tolong,
):
    return dlist_agregate_group(
        agregate_function   = sum,
        target_dlist        = target_dlist,
        agregate_field_list = sum_field_list,
        field_list          = field_list,
        convert             = lambda x: tolong(x, 0)
    )


def dlist_agregate_group(
    agregate_function,
    target_dlist,
    groupby_field_list = [],
    agregate_field_list = [],
    field_list = [],
    convert = lambda x: x
):

    if(not groupby_field_list):
        field_set = set(field_list)
        field_set_for_sum = set(agregate_field_list)
        field_set.difference_update(field_set_for_sum)
        groupby_field_list = list(field_set)


    def build_groupby_key_dict(item):
        return {
            field : item.get(field)
            for field in groupby_field_list
        }

    target_dlist = sorted(
        target_dlist,
        key=build_groupby_key_dict
    )

    prefetch = [
        (groupby_key_dict, list(for_agregate_generator))
        for groupby_key_dict, for_agregate_generator in groupby(
            target_dlist,
            key=build_groupby_key_dict
        )
    ]

    target_dlist = [
        dict(
            groupby_key_dict.items()
            + [
                (
                    field,
                    agregate_function(convert(fa_dict.get(field, 0))
                        for fa_dict in for_agregate_dlist)
                )
                for field in agregate_field_list
            ]
        )
        for groupby_key_dict, for_agregate_dlist in prefetch
    ]
    return target_dlist


def tolong(a, default = None):
    if(None == a):
        return default
    if isinstance(a, long):
        return a
    if isinstance(a, str) or isinstance(a, unicode):
        if(not check_isdigit(a)):
            return default
    try:
        return long(a)
    except:
        return default
    return default

def check_isdigit(s):
    if len(s) and s[0] in ('-', '+'):
        return s[1:].isdigit()
    return s.isdigit()