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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Should the `dict.get` overload with default value not be generic?","articleBody":"When using `dict.get` with a default value, it is expected that the key may not be found. Most of the time it's because we're not dealing with literal types, so we can't ensure that a key is part of the dict. But other times, it's we explicitely use a value that has a type we know won't be in range (often None).\r\n\r\nSee the example below (it is of course minimal and abstracted from a real-world example, but should still show the use):\r\n```py\r\ncode_events = {\r\n  0: \"ZERO_EVENT\",\r\n  1: \"ONE_EVENT\",\r\n  # ...\r\n  127: \"LAST_EVENT\",\r\n}\r\n\r\ndef parse_foo_code(self, code: int | None):\r\n  code  = code and (code \u0026 0x7f)  # Some bitwise operation to skip bit 8, this just shows we can't use -1 as default. And who knows what other keys could be used in the dict\r\n  event = code_events.get(code, \"SPECIAL_DEFAULT_FOO_EVENT\")\r\n  # ... do more with the event\r\n  \r\ndef parse_bar_code(self, code: int | None):\r\n  code  = code and (code \u0026 0x7f)  # Some bitwise operation to skip bit 8\r\n  event = code_events.get(code, \"SPECIAL_DEFAULT_BAR_EVENT\")\r\n  # ... do more with the event\r\n```\r\n\r\nCurrently it has to be written as such (without a cast). Which adds redundancy checks and no type-safety:\r\n```py\r\ndef parse_foo_code(self, code: int | None):\r\n  code  = code and (code \u0026 0x7f)  # Some bitwise operation to skip bit 8\r\n  if isinstance(code, int):  # You could imagine this could be more complex than just int. Maybe it can't even be easily expressed\r\n    event = code_events.get(code, \"SPECIAL_DEFAULT_FOO_EVENT\")\r\n  else:\r\n    event = \"SPECIAL_DEFAULT_FOO_EVENT\"\r\n  # ... do more with the event\r\n```\r\n\r\nWhat if this definition in dict:\r\n```py\r\n@overload\r\ndef get(self, __key: _KT) -\u003e _VT | None: ...\r\n@overload\r\ndef get(self, __key: _KT, __default: _VT | _T) -\u003e _VT | _T: ...\r\n```\r\n\r\nwas changed to:\r\n```py\r\n@overload\r\ndef get(self, __key: _KT) -\u003e _VT | None: ...\r\n@overload\r\ndef get(self, __key: object, __default: _VT | _T) -\u003e _VT | _T: ...  # Either object,  or Any if it causes variance issue.\r\n```\r\n\r\nWhat are your thoughts? Any reason this would be a bad idea? From what I can see there are legit sensible use-cases, it stays type-safe, and allows for more concise code. Or just use a cast and call it a day?","author":{"url":"https://github.com/Avasam","@type":"Person","name":"Avasam"},"datePublished":"2022-11-10T22:06:50.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/9155/typeshed/issues/9155"}