如何在 python 中显示 function 的 output？

Question

I`m trying to make a simple conversion program but the output keeps coming out either weird or none at all. How do I fix this? Here is my code.

#crypto = [Bitcoin, Ethereum, XRP, Litecoin]
bitcoin = [1, 40.19, 38284.22, 168.73]
ethereum = [.025, 1, 951.99, 4.20]
xrp = [.000026, .001, 1, .003]
litecoin = [.0058, .231, 223.81, 1]

def crypto2Crypto(x,y,w):
    if(x == "BE"):
        w =+ (y * bitcoin[1])
    if(x == "XL"):
        y * xrp[3]
    if(x == "EB"):
        y * ethereum[0]
    if(x == "LX"):
        y * litecoin[2]

def main():
    print("Welcome to the Cryptocurrency exchange!")
    conversion = input('"What will you be converting today? B = Bitcoin, E = Ethereum, X = XRP, Litecoin = L. Please give an exchange with the following syntax crypto1crypto2, ex. type "BE" for Bitcoin to Ethereum."')
    amountOfCurrency = float(input("How much do you have of " + conversion[0] + " ?"))
    w = crypto2Crypto(conversion,amountOfCurrency,0)
    print(w)
main()

Answer 1

Three problems

1. The =+ operators( yes, plural ) are not the same as the += operator.

   • An assignment ( = )

      >>> a = 2 >>> a =+ 1 >>> a 1

     Why? Because a =+ 1 becomes a = +1 ⇒ a = 1 .

   • An augmented assignment ( += )

      >>> a = 2 >>> a += 1 >>> a 3

     Why? Because a += 1 becomes a = a + 1 ⇒ a = 2 + 1 ⇒ a = 3 . More on augmented assignments here .

2. If you don't return some value from a function yourself, Python will automatically make it return None . So, you should add a return statement to crypto2Crypto . This has been shown in the solution in the next section.

3. Binary floating-point numbers (Python's float type, the one you used in main to get the value for amountOfCurrency ) and their arithmetic are not accurate. Read The Python Tutorial's chapter 15 for details.

Solution

Change the crypto2Crypto function to:

def crypto2Crypto(x, y, w):
    if x == "BE":
        w += (y * bitcoin[1])
    if x == "XL":
        w += (y * xrp[3])
    if x == "EB":
        w += (y * ethereum[0])
    if x == "LX":
        w += (y * litecoin[2])

    return w

As for the floating-point weirdness, you can use the built-in round function to round-off to the required number of decimal places.

Answer 2

Append this to the end of crypto2Crypto function

return w 

Not certain if w is what you need, but return what you need to