如何从函数的闭包中访问/修改变量？ [英] How do I access/modify variables from a function's closure?

问题描述

如果我有一个包含某些非局部变量的函数（在闭包中），我该如何访问该变量？我可以修改它吗？如果可以，如何修改？以下是此类函数的示例：

If I have a function which has some non-local variable (in a closure), how do I access that variable? Can I modify it, and if so, how? Here's an example of such a function:

def outer():
    x = 1
    def inner(y):
        nonlocal x
        return x + y
    return inner

inner = outer()
# how do I get / change the value of x inside inner?

（很抱歉，如果在其他地方已经回答过这个问题；我找不到它，所以我想我会一旦解决，就共享答案）

(apologies if this is already answered elsewhere; I couldn't find it, so I thought I would share the answer once I worked it out)

推荐答案

函数包含的变量作为元组存储在 __ closure __ 属性。变量以 cell 类型存储，这似乎只是变量本身的可变容器。您可以访问 cell 存储为 cell.cell_contents 的变量。由于单元格是可变的，因此您可以通过更改单元格内容来更改函数的非局部变量的值。例如：

A function's enclosed variables are stored as a tuple in the __closure__ attribute. The variables are stored as a cell type, which seems to just be a mutable container for the variable itself. You can access the variable a cell stores as cell.cell_contents. Because cells are mutable, you can change the values of a function's non-local variables by changing the cell contents. Here's an example:

def outer():
    x = 1
    def inner(y):
        nonlocal x
        return x + y
    return inner

inner = outer()

print(inner(2))  # 3
print(inner.__closure__)  # (<cell at 0x7f14356caf78: int object at 0x56487ab30380>,)
print(inner.__closure__[0].cell_contents)  # 1

inner.__closure__[0].cell_contents = 10
print(inner(2))  # 12
print(inner.__closure__[0].cell_contents)  # 10

编辑-以上答案适用于Python 3.7+。对于其他Python版本，您可以以相同的方式访问闭包，但是不能修改包含的变量（这是跟踪设置单元格值的Python问题）。

EDIT - the above answer applies to Python 3.7+. For other Python versions, you can access the closure the same way, but you can't modify the enclosed variables (here's the Python issue that tracked setting cell values).

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