Recursive dictionary merge in Python

merge_mappings.py

# Recursive dictionary merge
# Copyright (C) 2019 Brice Fernandes <brice.fernandes@gmail.com>
# 
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
from collections import Mapping
from functools import reduce

def merge_mappings(*args):
    def merge(a: Mapping, b: Mapping) -> Mapping:
        out = {**a}
        for k, _ in b.items():
            if (k in a and isinstance(a[k], Mapping) and isinstance(b[k], Mapping)):
                out[k] = merge(a[k], b[k])
            else:
                out[k] = b[k]
        return out
    return reduce(merge, args)