在python中使用lambda表达式在循环内部生成函数 [英] Generating functions inside loop with lambda expression in python
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问题描述
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 i
s.
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