python - 变量在某个地方失去了它的值(value)

Question

我一直在研究一个循环的罗马数字转换器，直到被告知退出并且它工作......在第一次迭代中。变量之后就是空的，这可能与我分配它的位置有关？

代码:

num_array = zip((1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1),
('M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V', 'IV', 'I'))

def int_to_roman(i):
    result = []
    for integer, numeral in num_array:
        count = int(i / integer)
        result.append(numeral * count)
        i -= integer * count
    return ''.join(result)

def roman_to_int(n):
    result = 0
    i = result
    for integer, numeral in num_array:
        while n[i:i + len(numeral)] == numeral:
            result += integer
            i += len(numeral)
    return result

x = ""
while x != "quit":
    x = ""
    x = input("enter number to be converted or quit to stop ")
    if x == "quit":
        break
    else:
        if x.isdigit():
            x = int(x)
            print(x, 'is',(int_to_roman(x)))
            print(' ')
        else:
            if x.isalpha():
                print(x,'is',(roman_to_int(x)))
                print(' ')

输出:

enter number to be converted or quit to stop C
C is 100

enter number to be converted or quit to stop C
C is 0

enter number to be converted or quit to stop 

Answer 1

在 Python3 中，zip 返回一个可迭代对象。第一次调用后，zip 的结果已经被消费了。您可以从 zip 的结果创建一个 list 而不是

num_array = list(zip((1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1),
                ('M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V',
                 'IV', 'I')))

用更小的例子更容易理解

>>> nums = zip((1, 2, 3, 4), ('A', 'B', 'C', 'D'))
>>> nums
<zip object at 0x7f5a860cba08>
>>> for item in nums:
...     print(item)
... 
(1, 'A')
(2, 'B')
(3, 'C')
(4, 'D')
>>> for item in nums:   # Nothing left in zip object
...     print(item)
... 
>>> nums = list(zip((1, 2, 3, 4), ('A', 'B', 'C', 'D')))
>>> nums
[(1, 'A'), (2, 'B'), (3, 'C'), (4, 'D')]
>>> for item in nums:
...     print(item)
... 
(1, 'A')
(2, 'B')
(3, 'C')
(4, 'D')
>>> for item in nums:   # Can loop over a list as many times as you like
...     print(item)
... 
(1, 'A')
(2, 'B')
(3, 'C')
(4, 'D')
>>>