python - 全局名称 'X' 未定义

Question

我查看了各种类似的问题，但找不到适合我情况的问题(或者也许有，但我是编程新手)。

我使用的 Python 版本是 2.7.4，我的程序在第 11 行出现错误:NameError: global name 'opp' is not defined

我想制作一个地板尺寸计算器。这是我的代码:

def oppervlakte():
    global lengte
    global br
    global opp

    lengte = raw_input("Voer de lengte in: ") # Put in the length
    br = raw_input("Voer de breedte in: ") # Put in the width
    opp = lengte * br # Calculates the dimension of the floor
    return int(lengte), int(br) # Makes the variables lengte & br an integer

print opp

既然得到了答案，就想和大家分享一下，所以在此:

def oppervlakte():
    lengte = raw_input("Voer de lengte in: ") # Asks for the length
    br = raw_input("Voer de breedte in: ") # Asks for the width

    lengte = int(lengte) # String lengte --> int lengte 
    br = int(br) # String br --> int br

    opp = lengte * br # Calculates the dimensions of the floor

    return opp, lengte, br

opp, lengte, br = oppervlakte()
print "De oppervlakte is", opp # Prints the dimension

Answer 1

你应该调用你的函数，否则 opp 将不会被定义。

oppervlakte()
print opp

但更好的方法是从函数返回 opp 并分配给全局命名空间中的变量。

def oppervlakte():
    lengte = int(raw_input("Voer de lengte in: ")) #call int() here
    br = int(raw_input("Voer de breedte in: ")) # call int() here
    opp = lengte * br # Calculates the dimension of the floor
    return opp, lengte, br 

opp, lengte, br = oppervlakte()

并且仅对字符串调用 int() 不会使其成为整数，您应该将返回值分配给变量。

>>> x = '123'
>>> int(x)       #returns a new value, doesn't affects `x`
123
>>> x            #x is still unchanged
'123'
>>> x = int(x)   #re-assign the returned value from int() to `x`
>>> x
123