dict_merge.py

from functools import reduce
from typing import Iterable

def dict_values_same_types(key, cls, *dicts):
    return all(isinstance(d[key], cls) for d in dicts)


def dict_merger(original: dict, incoming: dict):
    """
    In place deep merge `incoming` into `original`.
    **You probably want `merge_dicts`, this is a lower-level function used by it**
    Key conflict bevaviour:
        - `dict`: Recursively call dict_merger on both values
        - `int`: sum values
        - any other type: Override value in `original` with value in `incoming
    If values of same key have conflicting *type*, value in `original` overridden.
    """

    def type_match(key, cls):
        return dict_values_same_types(key, cls, original, incoming)

    for key in incoming:
        if key in original:
            if type_match(key, dict):
                dict_merger(original[key], incoming[key])
            # isinstance(True, int) == True, isinstance(1, bool) == False
            elif type_match(key, int) and not type_match(key, bool):
                original[key] += incoming[key]
            else:
                original[key] = incoming[key]
        else:
            original[key] = incoming[key]
    return original


def merge_dicts(*dicts: Iterable[dict]):
    """
    Deep merge `dicts` into a single new dict. **Warning**: this will modify
    `dicts` due to in place updates.
    """
    return reduce(dict_merger, dicts)

TODO:

• Handle lists
  • Merge instead of overwriting
• Allow 'merger' function for different types to be passed in to improve API
  • i.e. allow caller to specify that int's should be multiplied instead of added or strs should be concatenated instead of overwritten e.t.c