python - 关于Python中的变量赋值

Question

这里我写了两个简单的程序，并期望结果是相同的: 程序1(结果=123):

price=[]
def checkCondition(a,b):
    if a<b:
        price.append(123)
if  __name__ == '__main__':
    checkCondition(1,2)
print price[0]

程序 2(结果=''):

price=''
def checkCondition(a,b):
    if a<b:
        price=123
if  __name__ == '__main__':
    checkCondition(1,2)
print price

为什么它无法将 123 分配给程序 2 中的价格？

Answer 1

您正在分配一个局部变量。告诉 Python 使用全局变量:

price=''
def checkCondition(a,b):
    global price # now reassigning price
    if a<b:
        price=123
if  __name__ == '__main__':
    checkCondition(1,2)
print price

来自 Python 文档 Naming and binding :

If a name binding operation occurs anywhere within a code block, all uses of the name within the block are treated as references to the current block. [...]

If the global statement occurs within a block, all uses of the name specified in the statement refer to the binding of that name in the top-level namespace.