Meaning
This chunk creates a new dictionary by iterating over each key‑value pair of an existing dictionary and multiplying each value by two. It provides a concise way to transform all values while preserving the original keys. It is triggered when you need a derived mapping with modified values without writing an explicit loop.
Primary Function
Data transformation
Communicative Purpose
Enables rapid transformation of dictionary values by applying a uniform operation
Pattern
{key: value * 2 for key, value in source_dict.items()}
Core Structure
{...: ... * 2 for ..., ... in ... .items()}
Função primária
Data transformation
Propósito comunicativo
Enables rapid transformation of dictionary values by applying a uniform operation
Situações de gatilho
Data processing: need to double numeric values in a mapping; Configuration handling: adjust thresholds in a settings dict; Analytics: scale metric values stored in a dict
Contextos
General Python codebases, data‑science scripts, web back‑ends, configuration management modules
Padrão
{key: value * 2 for key, value in source_dict.items()}
Estrutura central
{...: ... * 2 for ..., ... in ... .items()}
Slots de substituição
key: hashable, value: any, source_dict: dict of key to value
Colocados típicos
- for ... in ...
- .items()
- dict comprehension
- multiplication operator
Substituições comuns
- use a for‑loop with dict assignment → more verbose
- use dict.update with a generator expression → similar result but less readable
Erros comuns
Using `*` on non‑numeric values → TypeError; forgetting `.items()` and iterating over keys only → only keys processed; reusing same variable names causing shadowing → unexpected results; omitting colon after key → SyntaxError
Similar / contraste
list comprehension (produces a list, not a dict); set comprehension (creates a set); dict.update (mutates existing dict); map function (returns iterator, not a dict)
Interferências
Coming from JavaScript: may try to use `Object.entries` with a for‑of loop → Python uses `.items()` instead
Família do chunk
- list comprehension
- set comprehension
- dict merging
- dict update
Nuance
Do not use when values are non‑numeric or when you need to keep the original dict unchanged; creates a new dict in O(n) time and memory, preserving key order as of Python 3.7; large dictionaries may increase memory pressure
Efeito pragmático
Allows concise, readable transformation of all dictionary values, reducing boilerplate and potential bugs
Dica de memória
Dictionary comprehension: like a factory that takes each raw ingredient (key, value) and outputs a packaged product (key, doubled value).
Nota
The comprehension evaluates each expression eagerly; for very large dictionaries consider generator‑based approaches to limit memory usage
Upgrade path
nested dictionary comprehension for transforming nested mappings
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