Python:动态定义函数 [英] Python: defining functions on the fly

问题描述

我有以下代码:

 funcs = []
 for i in range(10):
   def func():
      print i
   funcs.append(func)

 for f in funcs:
   f()

问题是func被覆盖.即代码的输出是:

The problem is that func is being overriden. Ie the output of the code is:

9
9
9
...

您如何在不定义新功能的情况下解决此问题?

How would you solve this without defining new functions?

最佳解决方案是更改函数的名称.即:

The optimal solution would be to change the name of the function. Ie:

for i in range(10):
   def func+i():
...

(或其他一些奇怪的语法)

(or some other weird syntax)

推荐答案

问题不在于func被覆盖，而是i的值是在调用函数时(而不是在定义函数时)进行求值的.如果要在定义时评估i，请将其作为默认参数作为func放在函数声明中.

The problem is not that func is being overwritten, it's that the value of i is being evaluated when the function is called, not when it is defined. If you want to evaluate i at definition time, put it in the function declaration, as a default argument to func.

funcs = []
for i in range(10):
    def func(value=i):
        print value
    funcs.append(func)

for f in funcs:
    f()

在定义函数时，默认参数将被评估一次，因此递增循环不会影响它们.如果您使用过，效果会一样好

Default arguments are evaluated once, when the function is defined, so the incrementing loop will not affect them. This would work just as well if you used

def func(i=i):
    print i

但是我使用名称value来明确函数中使用的名称.

but I used the name value to make it clear which name is being used within the function.

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