Question

我想确保输入为数字。我已尝试使用符号和字母进行测试，但shell只会抛出一个错误，上面写着“Decimal的文字无效”。我正在研究计算器，所以认为十进制模块最适合。提前谢谢。

这是我的代码：

import decimal

while True:
 userInput = (raw_input("Enter number:"))
 try:
  userInput = decimal.Decimal(userInput)
  break
 except ValueError:
  print ("Number please")

使用Python 2.7.6

Answer 1

Catch decimal.InvalidOperation

>>> a = 's'
>>> try:
...     decimal.Decimal(a)
... except decimal.InvalidOperation:
...     print 'fds'
... 
fds

Answer 2

不是抓住ValueError，而是抓住decimal.InvalidOperation错误。将无效数据传递给decimal.Decimal构造函数时会抛出此错误。

Answer 3

检查值是否为Decimal的有效输入的正确方法是：

from decimal import Decimal, DecimalException

try:
    Decimal(input_value)
except DecimalException:
    pass

https://docs.python.org/2/library/decimal.html#decimal.DecimalException

Answer 4

你正在捕捉错误的异常。您正在捕获ValueError，但代码会针对无效十进制值的各种输入抛出decimal.InvalidOperation。

>python test.py
Enter number:10

>python test.py
Enter number:10.2

>python test.py
Enter number:asdf
Traceback (most recent call last):
  File "test.py", line 6, in <module>
    userInput = decimal.Decimal(userInput)
  File "C:\Python27\lib\decimal.py", line 548, in __new__
    "Invalid literal for Decimal: %r" % value)
  File "C:\Python27\lib\decimal.py", line 3872, in _raise_error
    raise error(explanation)
decimal.InvalidOperation: Invalid literal for Decimal: 'asdf'

>python test.py
Enter number:10.23.23
Traceback (most recent call last):
  File "test.py", line 6, in <module>
    userInput = decimal.Decimal(userInput)
  File "C:\Python27\lib\decimal.py", line 548, in __new__
    "Invalid literal for Decimal: %r" % value)
  File "C:\Python27\lib\decimal.py", line 3872, in _raise_error
    raise error(explanation)
decimal.InvalidOperation: Invalid literal for Decimal: '10.23.23'

将except行更改为except decimal.InvalidOperation:

检查用户输入是否对十进制有效？

4 个答案: