Copy item from one dict to another supporting subdicts access using dots in keys

copy_key.py

from functools import reduce
from contextlib import suppress


def copy_key(src_dict, dst_dict, src_key, dst_key):
    _s, _d = src_dict, dst_dict
    with suppress(KeyError):
        if '.' in dst_key:
            *subkeys, dst_key = dst_key.split('.')
            dst_dict = reduce(lambda x, y: x.setdefault(y, {}), subkeys, dst_dict)
        if '.' in src_key:
            *subkeys, src_key = src_key.split('.')
            src_dict = reduce(lambda x, y: x[y], subkeys, src_dict)
        dst_dict[dst_key] = src_dict[src_key]
    return _s, _d


x = copy_key({'a':{'b':2}}, {}, 'a.b', 'a.b.c.d')[1]
assert x == {'a':{'b':{'c':{'d':2}}}}, x