程序功能改变

Question

我正在努力学习如何创建函数。如何将此代码更改为多个函数？你知道吗

purchase = input('Enter the amount of purchase: ')
statetaxes = purchase * 0.05
countytaxes = purchase * 0.025
totaltaxes = (statetaxes + countytaxes)
totalPurchase = (purchase + totaltaxes)

print('The amount of purchase is $'), format(purchase, ',.2f')
print('State tax: $'), format(statetaxes, ',.2f')
print('County tax: $'), format(countytaxes, ',.2f')
print('Total tax: $'), format(totaltaxes, ',.2f')
print('Total: $'), format(totalPurchase, ',.2f')

会是这样的吗：

def main():

    purchase = get_purchase
    statetaxes = get_state
    countytaxes = get_county
    totaltaxes = statetaxes + countytaxes
    totalPurchase = totaltaxes + purchase

    print('The amount of purchase is $', purchase)
    print('State tax: ', statetaxes)
    print('County tax: ', countytaxes)
    print('Total tax: ', totaltaxes)
    print('Total: $'. totalPurchase)

def get_purchase():
    purchase = float(input('Please enter the amount of purchase')
    return purchase

def get_state():
    state = purchase * 0.05
    return statetaxes

def get_county():
    countytaxes = purchase * 0.025
    return countytaxes

main()

是这样吗？如果不是，我哪里做错了？你知道吗

我在没有python解释器的情况下这样做，因为我现在正在使用平板电脑等待航班。你知道吗

编辑：我要做的是把顶层程序分成多个函数。当我输入此代码时：

def get_purchase():
    return float(input('Please enter the amount of purchase '))

def get_state():
    return purchase * 0.05


def get_county():
    return purchase * 0.025

def main():

    purchase = get_purchase()
    statetaxes = get_state()
    countytaxes = get_county()
    totaltaxes = statetaxes + countytaxes
    totalPurchase = totaltaxes + purchase

    print('The amount of purchase is $', purchase)
    print('State tax: ', statetaxes)
    print('County tax: ', countytaxes)
    print('Total tax: ', totaltaxes)
    print('Total: $'. totalPurchase)

main()

我得到这个错误：

Please enter the amount of purchase 5000
Traceback (most recent call last):
  File "salestax.py", line 49, in <module>
    main()
  File "salestax.py", line 38, in main
    statetaxes = get_state()
  File "salestax.py", line 27, in get_state
    return purchase * 0.05
NameError: name 'purchase' is not defined

我现在正在上飞机，但会在中途停留时再检查一下，看看我做错了什么。你知道吗

Answer 1

代码审查：

将main（）代码移到底部。你知道吗

def get_purchase(): 
    '''Use docstrings to describe the function'''
    # purchase = float(input('Please enter the amount of purchase')
    # return purchase # no need to assign and then return the assignment
    # just return what you'd otherwise assign:
    return float(input('Please enter the amount of purchase')) # was missing a )

def get_state():
    '''calculate and return state taxes'''
    # state = purchase * 0.05
    # return statetaxes # see a problem here? what is statetaxes?
    return purchase * 0.05 # there, it's fixed!

def get_county():
    # countytaxes = purchase * 0.025
    # return countytaxes
    return purchase * 0.025

所以我们把main（）移到了底部。你知道吗

def main():

    purchase = get_purchase() # now we're calling these with the ()'s
    statetaxes = get_state()
    countytaxes = get_county()
    totaltaxes = statetaxes + countytaxes
    totalPurchase = totaltaxes + purchase

    print('The amount of purchase is $', purchase)
    print('State tax: ', statetaxes)
    print('County tax: ', countytaxes)
    print('Total tax: ', totaltaxes)
    print('Total: $'. totalPurchase)

最后，在模块的底部，不要只调用main()，使用常见的Python习惯用法：

if __name__ == '__main__':
    main()

如果导入模块，它会阻止代码执行main（）。导入模块时，其__name__不再与'__main__'相关：What does if __name__ == "__main__": do?

Answer 2

这个答案跟在您修改代码之后，现在得到了一个运行时异常。你知道吗

函数defget_state()和get_county()都引用了名为purchase的变量，该变量不在函数的作用域中。你知道吗

您应该将purchase传递到每个函数中，如下所示：

def get_state(purchase):
    return purchase * 0.05

def get_county(purchase):
    return purchase * 0.025

def main():
    purchase = get_purchase()
    statetaxes = get_state(purchase)
    countytaxes = get_county(purchase)

还有其他方法可以做到这一点，例如基于类的方法，但是正如您所说的，您正在学习函数，这可能是一种方法。你知道吗

Answer 3

您需要通过添加左/右括号来调用函数：

purchase = get_purchase()

在get_state()中有state和statetaxes变量—您只想使用其中的一个。你知道吗

另外，作为mhawke mentioned，需要使get_state和get_county接受purchase参数，并在调用这些函数时将purchase从main传递给它们。你知道吗

除此之外，您的函数似乎正确地分隔了逻辑操作。你知道吗