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具体的には、リストのバックアップを作成し、そのリストにいくつかの変更を加え、すべての変更を3番目のリストに追加しますが、その後、さらに変更を加える前に最初のリストをバックアップでリセットします。変更を行い、3 番目のリストのすべてのコンテンツを最初のリストにコピーして戻します。残念ながら、別の関数で最初のリストを変更すると、バックアップも変更されるようです。を使用original = backupしてもうまくいきませんでした。も使用しませんでした

def setEqual(restore, backup):
    restore = []
    for number in backup:
        restore.append(number)

私の問題を解決します。バックアップからリストを正常に復元したにもかかわらず、元のリストを変更するたびにバックアップが変更されました。

この問題を解決するにはどうすればよいですか？

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2 に答える 2

8

あなたcopy.deepcopy()はこれが欲しいです。

于 2010-03-16T23:27:17.340 に答える
5

The first thing to understand is why that setEqual method can't work: you need to know how identifiers work. (Reading that link should be very helpful.) For a quick rundown with probably too much terminology: in your function, the parameter restore is bound to an object, and you are merely re-binding that identifier with the = operator. Here are some examples of binding the identifier restore to things.

# Bind the identifier `restore` to the number object 1.
restore = 1
# Bind the identifier `restore` to the string object 'Some string.'
# The original object that `restore` was bound to is unaffected.
restore = 'Some string.'

So, in your function, when you say:

restore = []

You are actually binding restore to a new list object you're creating. Because Python has function-local scoping, restore in your example is binding the function-local identifier restore to the new list. This will not change anything you're passing in to setEqual as restore. For example,

test_variable = 1
setEqual(test_variable, [1, 2, 3, 4])
# Passes, because the identifier test_variable
# CAN'T be rebound within this scope from setEqual.
assert test_variable == 1

Simplifying a bit, you can only bind identifiers in the currently executing scope -- you can never write a function like def set_foo_to_bar(foo, bar) that affects the scope outside of that function. As @Ignacio says, you can use something like a copy function to rebind the identifier in the current scope:

original = [1, 2, 3, 4]
backup = list(original) # Make a shallow copy of the original.
backup.remove(3)
assert original == [1, 2, 3, 4] # It's okay!
于 2010-03-17T00:04:03.873 に答える