{**dict1, **dict2}

Built-in Data Structures

Meaning

The expression creates a new dictionary by unpacking the key‑value pairs of two existing mappings. It solves the need for a concise, non‑mutating way to combine settings or data where later values should win on key collisions. Use it whenever you need to overlay one mapping onto another without altering the originals.

Primary Function

Dictionary merging

Communicative Purpose

Combine two mappings into a single mapping, preferring values from the second on duplicate keys.

Pattern

{**first, **second}

Core Structure

{..., ...}

Função primária

Dictionary merging

Propósito comunicativo

Combine two mappings into a single mapping, preferring values from the second on duplicate keys.

Situações de gatilho

Configuration handling: merging default settings with user overrides; Data aggregation: combining results from multiple sources with overlapping keys; Deployment setup: overlaying environment‑specific options onto a base configuration

Contextos

Python applications, especially in configuration handling, data processing pipelines, and API request/response building.

Padrão

{**first, **second}

Estrutura central

{..., ...}

Slots de substituição

dict1: first mapping, dict2: second mapping (overrides duplicates on key collision)

Colocados típicos

dict.update()
dictionary union operator (dict1 | dict2)
collections.ChainMap

Substituições comuns

dict1 | dict2 (Python 3.9+)
{**dict2
**dict1} (reverse order)
{k: v for d in (dict1
dict2) for k
v in d.items()}

Erros comuns

Assuming the operation mutates the original dictionaries; forgetting that later dict overrides earlier; applying to non-mapping objects causing TypeError.

Similar / contraste

dict.update() (mutates original dict), dict1 | dict2 (union operator, Python 3.9+), collections.ChainMap (provides a view without copying).

Interferências

Coming from JavaScript: similar to Object.assign({}, dict1, dict2) but note ordering; from C++: akin to merging std::map via insert or merge.

Família do chunk

dict unpacking
dict union operator
dict.update
collections.ChainMap

Nuance

Creates a shallow copy; nested dictionaries are referenced, not duplicated; if either operand is not a mapping, a TypeError is raised.

Efeito pragmático

Provides a concise, readable way to combine dictionaries without mutating the originals.

Dica de memória

Double splat merges: ** spreads dict contents into a new dict literal.

Nota

Creates a new dictionary with shallow copies of the values; original dictionaries remain unchanged; if either operand is not a mapping, a TypeError is raised.

Upgrade path

Use the dict union operator dict1 | dict2 (available in Python 3.9+) for an even more concise syntax.

Frequência: HighFormulaicidade: Semi-fixedTipo de construção: expressionPrioridade de aquisição: Active recallPrioridade de output: BothTag de espaçamento: Medium-termIdioma?: Sim

Examples

python # Merge default configuration with user overrides defaults = {"timeout": 30, "retries": 3, "debug": False} user_settings = {"timeout": 10, "theme": "dark"} config = {**defaults, **user_settings} print(config) # {'timeout': 10, 'retries': 3, 'debug': False, 'theme': 'dark'}

python # Combine results from two independent data sources source_a = {"id": 1, "name": "Alice", "score": 85} source_b = {"score": 90, "grade": "A"} merged = {**source_a, **source_b} print(merged) # {'id': 1, 'name': 'Alice', 'score': 90, 'grade': 'A'}

python # Building a configuration overlay from multiple layers base = {"host": "localhost", "port": 8080} dev_overlay = {"port": 8000, "reload": True} prod_overlay = {"host": "prod.example.com"} settings = {**base, **dev_overlay, **prod_overlay} print(settings) # {'host': 'prod.example.com', 'port': 8000, 'reload': True}