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  "description": "Learn how to create a Python sentinel value with the new built-in in Python 3.15 and get readable signatures, type hints, and safe copying and pickling.",
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        "name": "What is a sentinel value in Python?",
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          "text": "\u003cp\u003eA \u003ca href=\"/ref/computer-science-glossary/sentinel-value/\" class=\"ref-link\"\u003esentinel value\u003c/a\u003e is a value that your code treats as a signal rather than as data. It marks a condition such as \u0026ldquo;no argument was passed,\u0026rdquo; \u0026ldquo;nothing was found,\u0026rdquo; or \u0026ldquo;a loop should stop.\u0026rdquo; What matters is that it stays distinct from every legitimate value your data can take.\u003c/p\u003e"
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          "text": "\u003cp\u003eYou can call the \u003ccode\u003esentinel\u003c/code\u003e built-in with a string that names the marker, then assign the result to a variable with that same name. You don\u0026rsquo;t need an import because \u003ccode\u003esentinel\u003c/code\u003e lives in the built-in namespace. An optional \u003ccode\u003erepr\u003c/code\u003e keyword argument lets you display something other than the name.\u003c/p\u003e"
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        "name": "What problems does Python\u2019s sentinel built-in solve?",
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          "text": "\u003cp\u003eThe \u003ccode\u003esentinel\u003c/code\u003e built-in fixes the drawbacks of using \u003ccode\u003eobject()\u003c/code\u003e as a marker. It prints a readable name instead of a memory address, gives you a name you can use in a \u003ca href=\"/ref/glossary/type-hint/\" class=\"ref-link\"\u003etype hint\u003c/a\u003e, and keeps its identity through \u003ccode\u003ecopy()\u003c/code\u003e, \u003ccode\u003edeepcopy()\u003c/code\u003e, and a \u003ccode\u003epickle\u003c/code\u003e round trip. Because every sentinel is a unique object, no real data can equal one by accident.\u003c/p\u003e"
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          "text": "\u003cp\u003e\u003ccode\u003eNone\u003c/code\u003e is still the right default for most optional parameters. Use a sentinel when \u003ccode\u003eNone\u003c/code\u003e is legitimate data and you need a separate marker for \u0026ldquo;nothing was passed.\u0026rdquo; If you already use an \u003ccode\u003eobject()\u003c/code\u003e marker, switching to a sentinel pays off when the marker appears in a public signature or travels through \u003ccode\u003ecopy\u003c/code\u003e or \u003ccode\u003epickle\u003c/code\u003e. The guide on \u003ca href=\"https://realpython.com/null-in-python/\"\u003eusing null in Python\u003c/a\u003e covers \u003ccode\u003eNone\u003c/code\u003e and its common uses in more depth.\u003c/p\u003e"
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          "text": "\u003cp\u003eYes. A sentinel supports the \u003ccode\u003e|\u003c/code\u003e operator, so you can use its bare name in a union alongside real types, following the precedent set by \u003ccode\u003eNone\u003c/code\u003e years ago. The sentinel stands for a type whose only member is the sentinel object itself.\u003c/p\u003e"
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