April 2025
Intermediate to advanced
468 pages
14h 8m
Italian
Content preview from Python ad alte prestazioni, 2a edizione
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Capitolo 4. Dizionari e insiemi
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Gli insiemi e i dizionari sono strutture di dati ideali da utilizzare quando i dati non hanno un ordine intrinseco (ad eccezione dell'ordine di inserimento) ma hanno un oggetto univoco che può essere utilizzato per fare riferimento(l'oggetto di riferimento è normalmente una stringa, ma può essere di qualsiasi tipo hashable ). Questo oggetto di riferimento è chiamato chiave, mentre i dati sono il valore. I dizionari e gli insiemi sono quasi identici, tranne per il fatto che gli insiemi non contengono valori: un insieme è semplicemente una collezione di chiavi uniche. Come suggerisce il nome, gli insiemi sono molto utili per eseguire operazioni di tipo set.
Nota
Un tipo hashable è un tipo che implementa sia la funzione magica __hash__ sia __eq__ o __cmp__. Tutti i tipi nativi di Python li implementano già e le classi utente hanno dei valori predefiniti. Vedi"Funzioni Hash ed Entropia" per maggiori dettagli.
Mentre nel capitolo precedente abbiamo visto che siamo limitati, ...
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