{"topic":{"id":13343,"title":"Python local variable 我的知识盲点","slug":"topic","categoryId":4,"createdAt":"2024-09-03 10:58:37.764926","bumpedAt":"2024-09-03 10:58:38.007474","views":115,"postsCount":1,"highestPostNumber":1,"likeCount":0,"closed":false,"pinned":false,"pinnedGlobally":false,"pinnedAt":null,"pinnedUntil":null,"isBanner":false,"excerpt":"简单写个 Hanoi Tower： https://www.geeksforgeeks.org/problems/tower-of-hanoi-1587115621/1 同样是在函数里面用外面的变量，为啥 Pycharm 给 num_movements 标红，ret 不标红呢？问问 Github Copilot 得知： Q: why is var num_movements unaccessible while ret is acce…","deletedAt":null,"isAnonymous":false,"category":{"id":4,"name":"谈笑风生","slug":"general","color":"25AAE2"},"author":{"id":4668,"username":"IO","name":null,"avatarUrl":"/uploads/image/86/f2/86f267c0aaa73835a999b7cc3a7e7a701605574eda9a2c2a56f5ddbbba64d1a9.avif"},"tags":[]},"posts":[{"id":39390,"postNumber":1,"raw":"简单写个 Hanoi Tower：\n\n![Screenshot_20240903_185412|690x372](/uploads/image/90/5c/905ce65d4181c6a56c5505fea19db736184411e5179d5141eaaa03e169871b95.avif)\n\n同样是在函数里面用外面的变量，为啥 Pycharm 给 `num_movements` 标红，`ret` 不标红呢？\n\n\n问问 Github Copilot 得知：\n\nQ: why is var `num_movements` unaccessible while `ret` is accessible in function `my_toh`?\n\nA: The variable `num_movements` is inaccessible within the `my_toh` function because it is being **modified** inside the nested function, and Python treats it as a local variable within that scope. To modify a variable from an enclosing scope, you need to use the `nonlocal` keyword.\n\n\nQ: but why is var `ret` not treated aslocal variable?\nA: The variable `ret` is not treated as a local variable because it is not being modified within the nested function `my_toh`. In Python, variables that are **only read** within a nested function are considered to be from the enclosing scope unless explicitly declared as `global` or `nonlocal`. Since `ret` is only being **appended** to (which is a **method call** on the list object, not a reassignment), it is not considered a local variable within `my_toh`.","cooked":"

简单写个 Hanoi Tower：
\nhttps://www.geeksforgeeks.org/problems/tower-of-hanoi-1587115621/1
\n $\"Screenshot_20240903_185412\"$

同样是在函数里面用外面的变量，为啥 Pycharm 给 num_movements 标红，ret 不标红呢？

问问 Github Copilot 得知：

Q: why is var num_movements unaccessible while ret is accessible in function my_toh?

A: The variable num_movements is inaccessible within the my_toh function because it is being modified inside the nested function, and Python treats it as a local variable within that scope. To modify a variable from an enclosing scope, you need to use the nonlocal keyword.

Q: but why is var ret not treated aslocal variable?
\nA: The variable ret is not treated as a local variable because it is not being modified within the nested function my_toh. In Python, variables that are only read within a nested function are considered to be from the enclosing scope unless explicitly declared as global or nonlocal. Since ret is only being appended to (which is a method call on the list object, not a reassignment), it is not considered a local variable within my_toh.

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