Code Snippet — August 3, 2026 ### Python: Deep Merge — Recursive Dict Mer

🐍 Code Snippet — August 3, 2026

Python: Deep Merge — Recursive Dict Merge with Strategy Control

dict.update() and {a, b} flatten nested dicts. This gives you recursive merge, 4 list strategies, skip_keys for protected config, type coercion, custom conflict resolvers, and a diff() change preview. Zero deps.

from copy import deepcopy

def deep_merge(base, override, strategy="recursive",
               list_strategy="replace", skip_keys=None,
               type_coerce=False, on_conflict=None):
    result = deepcopy(base)
    for key, ov in override.items():
        if key in (skip_keys or set()): continue
        if key not in result:
            result[key] = ov; continue
        bv = result[key]
        if on_conflict: result[key] = on_conflict(key, bv, ov); continue
        if isinstance(bv, dict) and isinstance(ov, dict):
            if strategy == "recursive":
                result[key] = deep_merge(bv, ov, strategy,
                    list_strategy, skip_keys, type_coerce, on_conflict)
            else: result[key] = deepcopy(ov)
        elif isinstance(bv, list) and isinstance(ov, list):
            if list_strategy == "append": result[key] = bv + ov
            elif list_strategy == "prepend": result[key] = ov + bv
            elif list_strategy == "unique_append":
                result[key] = bv + [x for x in ov if x not in bv]
            else: result[key] = ov
        else: result[key] = ov
    return result

base = {"db": {"host": "localhost", "port": 5432}}
ovr  = {"db": {"host": "prod.db", "pool_size": 20}}
config = deep_merge(base, ovr)
# → {"db": {"host": "prod.db", "port": 5432, "pool_size": 20}}

# Protect secrets, append lists, coerce strings
deep_merge(a, b, skip_keys={"secret"}, list_strategy="append", type_coerce=True)

💡 Drop in config.py for layered config & env overrides. Full version w/ 10 self-tests in today's workspace.