Question

我是python的新手，这是我正在开发的第一个项目，它是一个Litecoin - Euro转换程序。我有一个问题，如果我没有把任何东西放到程序的Entry（）字段并提交它，控制台会输出以下错误信息（因为int（）和float（）不能将空字符串转换为int /一个浮动）：

Exception in Tkinter callback
Traceback (most recent call last):
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk/Tkinter.py", line 1536, in __call__
return self.func(*args)
File "/Users/Samir/Library/Mobile Documents/com~apple~CloudDocs/Coding/Python/hello_world/exch.py", line 13, in exchange
choice = int( exc.get() ) # choice of EUR to LTC or other way around
ValueError: invalid literal for int() with base 10: ''

我在这件事上使用的整个代码：

from Tkinter import *
from json import *
from urllib2 import *

def exchange():
    data = urlopen('https://btc-e.com/api/3/ticker/ltc_eur') # EUR - LTC API

    j_obj = load(data)  #loads json data
    exch = float( j_obj['ltc_eur']['avg'] ) # picks exchange rate out of api

    choice = int( exc.get() ) # choice whether EUR to LTC or other way around
    amount = float ( am.get() ) # amount of the currency the user wants to convert

    if choice == 0:
        print round((1 / exch) * amount, 2), "Litecoins"
    elif choice == 1:
        print round(exch * amount, 2), "Euro"
    else: # if something other than 0 or 1 was typed in
        print "I'm sorry but you have to enter either 0 or 1"

    am.delete(0, END)
    exc.delete(0, END)


master = Tk()   # creates new window in var master
master.wm_title("LTC - EUR converter")   # creates title for the window

Label(master, text = "EUR into LTC (0) or LTC into EUR(1): ").grid(row = 0, sticky = W) # creates choice string in a table (Row 1)
Label(master, text = "Amount: ").grid(row = 1, sticky = E)  # creates text "Amount" in a table (Row 1)

exc = Entry(master) # picks up Entryvalue
exc.grid(row = 0, column = 1)

am = Entry(master)  # picks up Entryvalue
am.grid(row = 1, column = 1)    # places it at row 0 colum 1 in the table

Button(master, text = "Quit", command = master.quit).grid(row = 2, column= 1, sticky = W)   # creates a quit button that closes the window
Button(master, text = "Submit", command = exchange).grid(row = 2, column = 1)   # creates a submit button that executes def "exchange"


mainloop() # starts the program

我设法修复了问题，更改了if查询，将输入与字符串进行比较，并在确认输入0或1之后将输入转换为int和float。更改的代码：

choice = exc.get()
amount = am.get()

if choice == '0':
    choice = int(choice)
    amount = float(amount)

    print round((1 / exch) * amount, 2), "Litecoins"
elif choice == '1':
    choice = int(choice)
    amount = float(amount)

    print round(exch * amount, 2), "Euro"
else:
    print "I'm sorry but you have to enter either 0 or 1"

所以我的问题是，这个问题的解决方案是否更有效？因为我认为我的方法有效，但它不是最好的选择。

Answer 1

"It is better to ask for forgiveness than permission".

您可以将代码放在try-except块中。

try:
    choice = int(choice)
    amount = float(amount)

except ValueError:
    print "I'm sorry but you have to enter either 0 or 1"
    return

if choice == 1:
    ...
else:
    ...

这样，您只需检查一次choice的值，而不是两次。

编辑：如果谨慎对try-except和choice保留单独的amount大括号。对于当前方案，输入有效的choice但无效的amount可能会产生误导性的错误消息。

ValueError：int（）的基数为10的文字无效：'

1 个答案: