问题描述
此问题摘自涉及Tkinter按钮的回调函数的原始应用程序.这是说明行为的一行.
This question is distilled from the original application involving callback functions for Tkinter buttons. This is one line that illustrates the behavior.
lambdas = [lambda: i for i in range(3)]
如果您随后尝试调用生成的lambda函数，请执行以下操作:lambdas[0]()，lambdas[1]()和lambdas[2]()都返回2.
if you then try invoking the lambda functions generated:lambdas[0](), lambdas[1]() and lambdas[2]() all return 2.
所需的行为是使lambdas[0]()返回0，lambdas[1]()返回1，lambdas[2])()返回2.
The desired behavior was to have lambdas[0]() return 0, lambdas[1]() return 1, lambdas[2])() return 2.
我看到index变量是通过引用解释的.问题是如何重新表述按价值对待.
I see that the index variable is interpreted by reference. The question is how to rephrase to have it treated by value.
推荐答案
您可以使用 functools.partial 可以从更通用的逐个应用程序创建专用功能，从而将参数数量减少一:
You can use functools.partial to create specialized functions from a more general one by partial application, which reduces the parameter count by one:
from functools import partial
lambdas = [partial(lambda x: x, i) for i in range(3)]
在这里，lambda x: x是带有一个参数的常规身份函数，您可以创建三个特殊化功能，不带任何参数，并返回固定值.
Here, lambda x: x is the general identity function taking one argument, and you create three specializations of it, taking no arguments, and returning fixed values.
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