在python中使用lambda表达式在循环内部生成函数

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如果我列出两个函数列表:

If I make two lists of functions:

def makeFun(i): return lambda: i a = [makeFun(i) for i in range(10)] b = [lambda: i for i in range(10)]

为什么列表a和b不能以保存方式运行?

why do lists a and b not behave in the save way?

例如:

>>> a[2]() 2 >>> b[2]() 9

推荐答案

从技术上讲，lambda表达式在全局范围内可见的i上 closed 关闭.在所有10个lambda中都引用了 same i.例如，

Technically, the lambda expression is closed over the i that's visible in the global scope, which is last set to 9. It's the same i being referred to in all 10 lambdas. For example,

i = 13 print b[3]()

在makeFun函数中，lambda在调用该函数时定义的i上关闭.那是十个不同 i s.

In the makeFun function, the lambda closes on the i that's defined when the function is invoked. Those are ten different is.