名称错误： 未定义全局名称'numKilos'

Question

def inputKilos():
    while True:
        numKilos = float(raw_input("Enter a number of Kilometers.  Enter 0 to end program. "))
        if numKilos == 0:
            break 
        else: 
            convert_kilos(numKilos)
    return
def convert_kilos(numKilos):
    numMiles = numKilos * 0.6214
    print_output()
    return
def print_output():
    print numKilos, "kilometers eqauls", numMiles, "miles."
def main():
    inputKilos()
main()

当我尝试运行该程序时，它说"名称错误：未定义全局名称'numKilos'"我不知道为什么它说未定义numKilos。 numKilos 等于用户输入的数字。

Answer 1

numKilos在

inputKilos和convert_kilos中都是局部变量，但不是print_output。局部变量只能从该函数中访问。

要传递变量，请使用 return <value> 从函数返回值，然后使用 result = function() 收集它，或者通过将值传递到函数中来执行相反的操作（就像您对 convert_kilos 所做的那样。

Answer 2

这些是局部变量，不是全局变量。

你可以试试这个：

#!/usr/bin/python
def inputKilos():
    while True:
        numKilos = float(raw_input("Enter a number of Kilometers.  Enter 0 to end program. "))
        if numKilos == 0:
            break 
        else: 
            miles = convert_kilos(numKilos)
            print_output(numKilos,miles)
    return
def convert_kilos(numKilos):
    numMiles = numKilos * 0.6214
    return numMiles
def print_output(numKilos,numMiles):
    print numKilos, "kilometers eqauls", numMiles, "miles."

inputKilos()

或使用全局关键字：

#!/usr/bin/python
numKilos=0
numMiles=0
def inputKilos():
    while True:
        global numKilos
        numKilos = float(raw_input("Enter a number of Kilometers.  Enter 0 to end program. "))
        if numKilos == 0:
            break 
        else: 
            convert_kilos(numKilos)
            print_output
def convert_kilos(numKilos):
    global numKilos
    global numMiles
    numMiles = numKilos * 0.6214    
def print_output:
    global numKilos
    global numMiles
    print numKilos, "kilometers eqauls", numMiles, "miles."

inputKilos()

Answer 3

这是一个重构版本：

MILES_PER_KM = 0.621371
def get_float(prompt=''):
    while True:
        try:
            return float(raw_input(prompt))
        except ValueError:
            pass
def main():
    while True:
        kms = get_float('Enter a distance in kms (or 0 to exit): ')
        if kms:
            miles = MILES_PER_KM * kms
            print '  {} kilometers is {} miles.'.format(kms, miles)
        else:
            break
if __name__=='__main__':
    main()