IF语句错误新变量输入python

Question

这里的问题是，我只是无法得到python来检查如果Currency1是在字符串，如果它不是然后打印，有一个错误，但如果Currency1 IS字符串然后移动和要求用户输入Currency2，然后再次检查。

Answer 1

您可以使用try-except：

def get_currency(msg): 
    curr = input(msg) 
    try: 
     float(curr) 
     print('You must enter text. Numerical values are not accepted at this stage') 
     return get_currency(msg) #ask for input again 
    except: 
     return curr    #valid input, return the currency name 

curr1=get_currency('Please enter the currency you would like to convert:') 
curr2=get_currency('Please enter the currency you would like to convert into:') 
ExRate = float(input('Please enter the exchange rate in the order of, 1 '+curr1+' = '+curr2)) 
Amount = float(input('Please enter the amount you would like to convert:')) 
print (Amount*ExRate) 

输出：

$ python3 foo.py 

Please enter the currency you would like to convert:123 
You must enter text. Numerical values are not accepted at this stage 
Please enter the currency you would like to convert:rupee 
Please enter the currency you would like to convert into:100 
You must enter text. Numerical values are not accepted at this stage 
Please enter the currency you would like to convert into:dollar 
Please enter the exchange rate in the order of, 1 rupee = dollar 50 
Please enter the amount you would like to convert: 10 
500.0 

Answer 2

你竟然试图为：

if type(Currency1) in (float, int): 
    ... 

但isinstance是更好地在这里：

if isinstance(Currency1,(float,int)): 
    ... 

，甚至更好，你可以使用numbers.Number抽象基类：

import numbers 
if isinstance(Currency1,numbers.Number): 

---

虽然... Currency1 = str(raw_input(...))将保证Currency1是一个字符串（不是整数或浮点数）。实际上，raw_input作出了保证，额外str这里只是多余的:-)。

如果你想检查功能字符串是否可以转换为数字，那么我认为最简单的方法是将只是尝试一下，看看：

def is_float_or_int(s): 
    try: 
     float(s) 
     return True 
    except ValueError: 
     return False