Question

我希望能够更改从英里到公里的距离列表，其中的里程列表在下面的代码中获得：

input_string = input("Enter a list of distances, separated by spaces").strip()

要将输入列表更改为整数列表，我使用了：

distances = input_string.split()
print("This is what you entered: ")
for distance in distances:
     print(distance)

def str2int(word):
    """Converts the list of string of miles into a list of integers of miles"""
    integer = int(word)
    if int(word):
        return integer
    else:
        sys.exit("Please try again and enter a list of integers.")


def validate_all(distances):
    """
    Checks if all the inputs are integers. If not all are integers, sys.exit
    without converting any of the distances and ask to try again.
    """

    true_list = []

    for distance in distances:
        if str2int(distance):
            true_list.append(distance)

    if len(distances) == len(true_list):
        return True
    else:
        return False

print("And now, we are going to convert the first one to kilometers:")
miles = distances[0]

if validate_all:
    # now, the calculation and display
    kms = miles_int * KMPERMILE
    print("The first distance you entered, in kilometers:", kms)

    for i in range(1, len(distances), 1):
        miles_int = str2int(distances[i])
        kms = miles_int * KMPERMILE
        print("The next distance you entered in kilometres:", kms)

但是，当我尝试检查字符串列表中的所有元素是否都可以更改为整数（使用validate_all（word））并且具有类似

的内容时

12 23 apples banana 5

作为我的输入，程序崩溃说

有值错误

str2int(word)
-> if int(word):

而不是我获取sys.exit

任何人都可以为我调试这个/请为我做这个吗？

Answer 1

>>> t = '12 23 apples banana 5'
>>> [int(x) for x in t.split() if x.isdecimal()]
[12, 23, 5]

Answer 2

您可以使用try-except子句：

def str2int(word):
    """Converts the list of string of miles into a list of integers of miles"""
    try:
        integer = int(word)
        return integer
    except ValueError:
        print "here"
        sys.exit("Please try again and enter a list of integers.")

print(str2int("asd"))

<强>输出：

here
Please try again and enter a list of integers.

注意：

您可以在Python docs中详细了解处理例外情况和try-except条款。

Answer 3

您尝试if int(x): ...，但int不是谓词。如果x是一个无法转换为int的字符串，则会引发ValueError。例如，x='0' if int(x): ...被评估为False，尽管它是类似int的值。

您需要的是以下谓词：

def is_int_able(x):
  try:
     int(x)
     return True
  except ValueError:
     return False

有了这个，你可以这样做：

[ int(x) for x in line.split() if is_int_able(x) ]

Answer 4

您的validate_all() 可以使用all()和str.digit()：

In [1]: all(e.isdigit() for e in ['12', '23', 'apples', 'banana', '5'])
Out[1]: False

In [2]: all(e.isdigit() for e in ['12', '23', '5'])
Out[2]: True

但也许更好的方法是取消此验证并在列表理解中使用if过滤：

In [3]: distances = ['12', '23', 'apples', 'banana', '5']

In [4]: [int(km) * km_to_miles for km in distances if km.isdigit()]
Out[4]: [7.456454304, 14.291537416, 3.10685596]

python中的字符串到整数函数

4 个答案: