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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def group(self, p_todos):
 """ Groups the todos according to the given group string. """

        # preorder todos for the group sort
        p_todos = _apply_sort_functions(p_todos, self.pregroupfunctions)

        # initialize result with a single group
        result = OrderedDict([((), p_todos)])

        for (function, label), _ in self.groupfunctions:
            oldresult = result
            result = OrderedDict()
            for oldkey, oldgroup in oldresult.items():
                for key, _group in groupby(oldgroup, function):
                    newgroup = list(_group)

                    if not isinstance(key, list):
                        key = [key]

                    for subkey in key:
                        subkey = "{}: {}".format(label, subkey)
                        newkey = oldkey + (subkey,)

                        if newkey in result:
                            result[newkey] = result[newkey] + newgroup
                        else:
                            result[newkey] = newgroup

        # sort all groups
        for key, _group in result.items():
            result[key] = self.sort(_group)

        return result