Question

如何确保用户只输入了一个包含两位小数的浮点数。数字不能是4或4.999，必须是4.00或4.99否则会出现错误。

while looping:
    try:
        number = float(input("Number: "))

        string_number = (str(number)).split(".")
        check_length = len(string_number)
        if check_length != 2:
            print ("ERROR!")
            looping = True
        else:
            looping = False

     except ValueError:
         looping = True

Answer 1

您目前只检查当前只有一个小数点。

number.split(".")将返回一个列表。如果number为4.323，则会返回['4', '323']。

您真正要在if子句中检查的是第二个元素的长度是2。

if len(string_number[1]) != 2:

Answer 2

检查号码的第二部分。

while True:
    try:
        number = input('Number:')
        integral, fractional = number.split('.')
        number = float(number)
        if len(fractional) == 2:
            break
    except ValueError:
        pass
    print('ERROR!')

Answer 3

looping = True
while looping:
    number = input("Number: ")
    string_number = number.split(".")
    if len(string_number) != 2:
        print ("ERROR: Needs exactly one decimal point!")
        looping = True
    elif len(string_number[1]) != 2:
        print ("ERROR: Two numbers are required after decimal point!")
        looping = True
    else:
        try:
            number = float(number)
            looping = False
        except ValueError:
            print("ERROR: Number is not valid!")
            looping = True

进行一些小的更改消除了变量looping的需要。由于我们的目标是获得有效数字，我们可以测试一下：

number = None
while not number:
    s = input("Number: ")
    string_number = s.split(".")
    if len(string_number) != 2:
        print ("ERROR: Needs exactly one decimal point!")
        continue
    elif len(string_number[1]) != 2:
        print ("ERROR: Two numbers are required after decimal point!")
        continue
    try:
        number = float(s)
    except ValueError:
        print("ERROR: Number is not valid!")

Answer 4

我会这样写：

while True:
    try: 
        str_num=input("Number: ")
        num=float(str_num)           # ValueError if cannot be converted
        i, f=str_num.split('.')      # also ValueError if not two parts
        if len(f)==2:
            break                    # we are done!!!
    except ValueError:
        pass

    print('ERROR! ')                 # either cannot be converted or not 2 decimal places

print(num)

Python：用户输入数字后只有两位小数

4 个答案: