{"id":1669,"date":"2025-09-30T22:54:33","date_gmt":"2025-09-30T15:54:33","guid":{"rendered":"https:\/\/kienthucmo.com\/?p=1669"},"modified":"2025-11-05T23:45:55","modified_gmt":"2025-11-05T16:45:55","slug":"tim-kiem-phan-tu-trong-dictionary-voi-python","status":"publish","type":"post","link":"https:\/\/kienthucmo.com\/vi\/tim-kiem-phan-tu-trong-dictionary-voi-python\/","title":{"rendered":"T\u00ecm ki\u1ebfm ph\u1ea7n t\u1eed trong Dictionary v\u1edbi Python"},"content":{"rendered":"\n

Dictionary (dict<\/code>) l\u00e0 c\u1ea5u tr\u00fac d\u1eef li\u1ec7u c\u1ef1c k\u1ef3 ph\u1ed5 bi\u1ebfn trong Python v\u00ec kh\u1ea3 n\u0103ng \u00e1nh x\u1ea1 nhanh gi\u1eefa key \u2192 value<\/strong>. Trong th\u1ef1c t\u1ebf m\u00ecnh th\u01b0\u1eddng d\u00f9ng dict<\/code> \u0111\u1ec3 l\u01b0u config, h\u1ed3 s\u01a1 ng\u01b0\u1eddi d\u00f9ng, cache t\u1ea1m,… v\u00e0 b\u00e0i to\u00e1n t\u00ecm ki\u1ebfm<\/strong> xu\u1ea5t hi\u1ec7n \u1edf m\u1ecdi n\u01a1i: ki\u1ec3m tra t\u1ed3n t\u1ea1i key, l\u1ea5y value an to\u00e0n, l\u1ecdc theo \u0111i\u1ec1u ki\u1ec7n, ho\u1eb7c t\u00ecm trong c\u1ea5u tr\u00fac l\u1ed3ng nhau.<\/p>\n\n\n\n

B\u00e0i vi\u1ebft n\u00e0y m\u00ecnh c\u00f9ng b\u1ea1n s\u1ebd t\u00ecm hi\u1ec3u chi ti\u1ebft c\u00e1c ph\u01b0\u01a1ng ph\u00e1p t\u00ecm ki\u1ebfm trong dictionary, t\u1eeb c\u01a1 b\u1ea3n \u0111\u1ebfn n\u00e2ng cao, th\u00f4ng qua nh\u1eefng v\u00ed d\u1ee5 minh h\u1ecda v\u00e0 gi\u1ea3i th\u00edch r\u00f5 r\u00e0ng. Hy v\u1ecdng r\u1eb1ng sau khi \u0111\u1ecdc xong, ch\u00fang ta s\u1ebd n\u1eafm v\u1eefng c\u00e1ch x\u1eed l\u00fd c\u00e1c t\u00ecnh hu\u1ed1ng t\u00ecm ki\u1ebfm trong th\u1ef1c t\u1ebf.<\/p>\n\n\n\n

1. C\u00e1ch dict<\/code> ho\u1ea1t \u0111\u1ed9ng v\u00e0 \u00fd ngh\u0129a khi t\u00ecm ki\u1ebfm<\/h2>\n\n\n\n

Tr\u01b0\u1edbc khi \u0111i v\u00e0o k\u1ef9 thu\u1eadt, c\u1ea7n nh\u1edb v\u00e0i \u0111i\u1ec3m n\u1ec1n t\u1ea3ng:<\/p>\n\n\n\n

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  • dict<\/code> d\u00f9ng hash table<\/strong>: lookup theo key<\/strong> trung b\u00ecnh l\u00e0 O(1)<\/strong> (average-case).<\/li>\n\n\n\n
  • Key ph\u1ea3i hashable<\/strong> (immutable types: str<\/code>, int<\/code>, tuple<\/code> n\u1ebfu tuple c\u00e1c ph\u1ea7n t\u1eed hashable). Mutable types nh\u01b0 list<\/code> kh\u00f4ng th\u1ec3 l\u00e0m key.<\/li>\n\n\n\n
  • T\u00ecm value<\/strong> (kh\u00f4ng ph\u1ea3i key) th\u01b0\u1eddng ph\u1ea3i duy\u1ec7t to\u00e0n b\u1ed9 dict<\/code> \u2192 O(n)<\/strong>.<\/li>\n<\/ul>\n\n\n\n

    Hi\u1ec3u r\u00f5 \u0111i\u1ec1u n\u00e0y gi\u00fap l\u1ef1a ch\u1ecdn \u0111\u00fang ph\u01b0\u01a1ng ph\u00e1p: n\u1ebfu b\u1ea1n search theo key \u2014 d\u00f9ng lookup tr\u1ef1c ti\u1ebfp; n\u1ebfu b\u1ea1n c\u1ea7n l\u1ecdc theo value nhi\u1ec1u l\u1ea7n \u2014 c\u00e2n nh\u1eafc indexing ngo\u00e0i (v\u00ed d\u1ee5 inverted index).<\/p>\n\n\n\n

    2. T\u00ecm theo key<\/strong>: in<\/code>, []<\/code>, get()<\/code> v\u00e0 KeyError<\/code><\/h2>\n\n\n\n

    C\u00e1c thao t\u00e1c ph\u1ed5 bi\u1ebfn:<\/p>\n\n\n\n

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    • key in my_dict<\/code> \u2014 tr\u1ea3 True\/False<\/code>. R\u1ea5t nhanh (O(1) average).<\/li>\n\n\n\n
    • my_dict[key]<\/code> \u2014 tr\u1ea3 value ho\u1eb7c KeyError<\/strong> n\u1ebfu kh\u00f4ng t\u1ed3n t\u1ea1i.<\/li>\n\n\n\n
    • my_dict.get(key, default)<\/code> \u2014 tr\u1ea3 value ho\u1eb7c default (kh\u00f4ng raise l\u1ed7i).<\/li>\n<\/ul>\n\n\n\n

      V\u00ed d\u1ee5:<\/p>\n\n\n\n

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