Meaning
Creates a new dictionary containing only the entries from `mapping` whose values are positive, with each value doubled.
Primary Function
Filter and transform a mapping by selecting positive values and doubling them.
Communicative Purpose
Express a transformation that selects positive entries and scales their values.
Pattern
{k: v*2 for k, v in mapping.items() if v > 0}
Core Structure
{key: expression for key, value in iterable if condition}
Função primária
Filter and transform a mapping by selecting positive values and doubling them.
Propósito comunicativo
Express a transformation that selects positive entries and scales their values.
Situações de gatilho
When you need to filter out non‑positive values and scale the remaining values, e.g., normalizing positive counts or scaling scores.
Contextos
Data processing pipelines, score normalization, filtering positive measurements, preparing data for visualization.
Padrão
{k: v*2 for k, v in mapping.items() if v > 0}
Estrutura central
{key: expression for key, value in iterable if condition}
Slots de substituição
{mapping}: any iterable of key‑value pairs (e.g., dict.items()); {expression}: any expression using the value (e.g., v*2, v+1); {condition}: any boolean expression (e.g., v>0, v%2==0).
Colocados típicos
- dict
- mapping
- items
- filter
- map
- comprehension
Substituições comuns
- Expression: v*2 → v+1
- v*3
- v/2
- Condition: v>0 → v!=0
- v<10
- v%2==0
- Iterable: mapping.items() → enumerate(seq)
- zip(keys
- vals)
- Key expression: k → k.upper()
- k+'_suffix'.
Erros comuns
Using v*2 on non‑numeric values raises TypeError; forgetting .items() and iterating over keys only; omitting the condition and processing zero/negative values; using .values() and losing the keys.
Similar / contraste
Similar: {k: v for k, v in mapping.items() if v>0} (filter only); {k: v*2 for k, v in mapping.items()} (transform all); {k: v for k, v in mapping.items()} (identity). Contrasting: {k: v*2 for k, v in mapping.items() if v<0} (double negatives).
Interferências
Confusing with list/set comprehensions; misplacing the condition after the expression; using .items() on non‑mapping objects leads to AttributeError.
Família do chunk
- dict comprehension idioms
Nuance
Only values strictly greater than zero are processed; zero and negative values are omitted entirely.
Efeito pragmático
Signals the intent to keep only positive‑valued entries and scale them, often for normalization or emphasis.
Dica de memória
Double the positives.
Nota
Assumes the values support multiplication by an int; otherwise a TypeError is raised.
Upgrade path
Extend to more complex transformations (nested comprehensions, conditional expressions) or combine with other comprehensions.
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