为什么变量名“sum"导致错误 [Python] [英] why variable name "sum" cause error [Python]

问题描述

我为 Leetcode 问题

class Solution(object):
def addDigits(self, num):
    """
    :type num: int
    :rtype: int
    """
    while(1):
        if num in list( range(0,10) ):
            return num

        sum = sum( int(i) for i in str(num) )

        num = sum

它产生了一个错误Line 11: UnboundLocalError: local variable 'sum' referenced before assignment.它是通过将变量 sum 更改为 sum1 来修复的.

It yielded an error Line 11: UnboundLocalError: local variable 'sum' referenced before assignment. It was be fixed by changing variable sum to sum1.

sum 不在 非法变量列表中名称(关键字)(第 2.3 节).

sum is not in the list of illegal variable names (keywords) (section 2.3).

为什么会出错?是不是，当python看到sum = sum(...)时，python开始把sum当作一个变量而忘记它是一个函数?

So why error? Is it that, when python sees sum = sum(...), python starts to treat sum as a variable and forget it's a function?

推荐答案

您绝对可以将变量称为sum"、file"和reduce".如果您在全局范围内执行此操作，它确实会起作用.例如:

You can definitely call your variables "sum","file" and "reduce". And it will really work if you are doing it in the global scope. For example :

In [6]: sum = sum(range(1,10))

sum 将等于 45，一切都很好.(尽管您不能再使用函数 sum.)

sum will equal 45 and everything is great. (Despite the fact you can't use function sum anymore.)

但是当您尝试在函数内部使用它时:解释器为函数内部定义的变量定义了它自己的范围.

But when you are trying to use this inside the function : interpreter defines it's own scope for variables defined inside the function.

In [2]: def f():
   print type(sum)
   sum = sum(range(1,10))
f()

您可能期望答案是builtin_function_or_method"，但实际上您会得到与上述相同的错误.希望有人对python解释器的细节提供更好的解释.

You may expect the answer will be "builtin_function_or_method" but actually you will get the same error as above. Hope someone will provide better explanation for the details of python interpreter.

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