编程新手，不明白为什么我不能得到这个变量来打印

Question

每当我运行这段代码，它告诉我在第19行distancetravelled没有被定义，但我想我已经在函数中定义了它。谢谢你的帮助。

startKilometre = float(input("What is the starting kilometre?")) 
finalKilometre = float(input("What is the final kilomotre")) 
finalFuel = float(input("How much fuel did you put in the car?")) 

def functionTravelled(startKilometre, finalKilometre): 
    distanceTravelled = finalKilometre - startKilometre 
    return distanceTravelled 



def functionLitresKilo(distanceTravelled, finalFuel): 
    litresPerKilometre = distanceTravelled/finalFuel 
    return litresPerKilometre 

def functionKiloLitres(finalFuel, distanceTravelled): 
    kilometresPerLitre = finalFuel/distanceTravelled 
    return kilometresPerLitre 

print(distanceTravelled) 
print(litersPerKilometre) 
print(kilometresPerLitre) 

Answer 1

你永远不会调用函数来获取他们的返回值，因此，您的代码运行，如：

startKilometre = float(input("What is the starting kilometre?")) 
finalKilometre = float(input("What is the final kilomotre")) 
finalFuel = float(input("How much fuel did you put in the car?")) 

print(distanceTravelled) 
print(litersPerKilometre) 
print(kilometresPerLitre) 

其中，当然，是不是你想要的。你需要调用每个函数，并返回结果存储在变量中：

startKilometre = float(input("What is the starting kilometre?")) 
finalKilometre = float(input("What is the final kilomotre")) 
finalFuel = float(input("How much fuel did you put in the car?")) 

def functionTravelled(startKilometre, finalKilometre): 
    distanceTravelled = finalKilometre - startKilometre 
    return distanceTravelled 

def functionLitresKilo(distanceTravelled, finalFuel): 
    litresPerKilometre = distanceTravelled/finalFuel 
    return litresPerKilometre 

def functionKiloLitres(finalFuel, distanceTravelled): 
    kilometresPerLitre = finalFuel/distanceTravelled 
    return kilometresPerLitre 

distanceTravelled = functionTravelled(startKilometre, finalKilometre) 
litersPerKilometre = functionLitresKilo(distanceTravelled, finalFuel) 
kilometresPerLitre = functionKiloLitres(finalFuel, distanceTravelled) 

print(distanceTravelled) 
print(litersPerKilometre) 
print(kilometresPerLitre) 

Answer 2

您试图打印一个不存在的变量。该变量在您的functionTravelled函数中进行本地定义。你想打印这些函数返回的内容（并且你永远不会真的调用你的函数）。

例如 -

startKilometre = float(input("What is the starting kilometre?")) 
finalKilometre = float(input("What is the final kilomotre")) 
finalFuel = float(input("How much fuel did you put in the car?")) 

def functionTravelled(startKilometre, finalKilometre): 
    distanceTravelled = finalKilometre - startKilometre 
    return distanceTravelled 

travelled = functionTravelled(startKilometre, finalKilometre) 
print(travelled) 

同样为您的其他打印语句/函数。

Answer 3

有点像“什么在拉斯维加斯的推移，留在拉斯维加斯”，你定义的函数的变量，它是不可见的外功能。这是有目的的完成的，所以你不必担心在函数中为变量使用唯一的名称。

您的函数是为返回变量的值而构建的，因此只需调用它们即可。在这里，我通过调用函数在全局范围内分配变量。

startKilometre = float(input("What is the starting kilometre?")) 
finalKilometre = float(input("What is the final kilomotre")) 
finalFuel = float(input("How much fuel did you put in the car?")) 

def functionTravelled(startKilometre, finalKilometre): 
    distanceTravelled = finalKilometre - startKilometre 
    return distanceTravelled 



def functionLitresKilo(distanceTravelled, finalFuel): 
    litresPerKilometre = distanceTravelled/finalFuel 
    return litresPerKilometre 

def functionKiloLitres(finalFuel, distanceTravelled): 
    kilometresPerLitre = finalFuel/distanceTravelled 
    return kilometresPerLitre 

distanceTravelled = functionTravelled(startKilometre, finalKilometre) 
print(distanceTravelled) 

etc.... 

Answer 4

看起来您需要对函数的定义和调用做更多的研究。你正在将它们想象成为了有趣的代码块，并没有实际的理由被使用。不是这种情况。函数被定义，然后被调用，在这一点上他们返回一个值给调用者。下面是不是一个函数：

a = 0 
print(a) 

将其组合成一个功能不相同的方式工作，如在这个精简版，你在做什么：

def x(): 
    a = 0 
    return a 
print(a) 

功能必须通过他们的实际名字叫，你可能希望保存得到的返回值：

def x(): 
    a = 0 
    return a 
var = x() 
print(var) 

您可以了解更多关于the official tutorial's section on defining functions功能，以及对T许多其他地方他互联网，如果你运行谷歌搜索如何定义和使用Python中的功能。