如何检查输入是否为 Python 中的数字？
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How do I check if input is a number in Python?
提问by RoyalSwish
I have a Python script which converts a decimal number into a binary one and this obviously uses their input.
我有一个 Python 脚本，它将十进制数转换为二进制数，这显然使用了它们的输入。
I would like to have the script validate that the input is a number and not anything else which will stop the script.
我想让脚本验证输入是一个数字，而不是其他任何会停止脚本的东西。
I have tried an if/else statement but I don't really know how to go about it. I have tried if decimal.isint():and if decimal.isalpha():but they just throw up errors when I enter a string.
我试过 if/else 语句，但我真的不知道如何去做。我试过了if decimal.isint():，if decimal.isalpha():但是当我输入一个字符串时，他们只是抛出错误。
print("Welcome to the Decimal to Binary converter!")
while True:
print("Type a decimal number you wish to convert:")
decimal = int(input())
if decimal.isint():
binary = bin(decimal)[2:]
print(binary)
else:
print("Please enter a number.")
Without the if/else statement, the code works just fine and does its job.
如果没有 if/else 语句，代码就可以正常工作并完成它的工作。
采纳答案by Martijn Pieters
If the int()call succeeded, decimalis alreadya number. You can only call .isdigit()(the correct name) on a string:
如果int()调用成功，decimal则已经是一个号码。您只能.isdigit()在字符串上调用（正确的名称）：
decimal = input()
if decimal.isdigit():
decimal = int(decimal)
The alternative is to use exception handling; if a ValueErroris thrown, the input was not a number:
另一种方法是使用异常处理；如果ValueError抛出 a，则输入不是数字：
while True:
print("Type a decimal number you wish to convert:")
try:
decimal = int(input())
except ValueError:
print("Please enter a number.")
continue
binary = bin(decimal)[2:]
Instead of using the bin()function and removing the starting 0b, you could also use the format()function, using the 'b'format, to format an integer as a binary string, without the leading text:
除了使用bin()函数并删除起始0b，您还可以使用format()函数，使用'b'格式，将整数格式化为二进制字符串，没有前导文本：
>>> format(10, 'b')
'1010'
The format()function makes it easy to add leading zeros:
该format()函数可以轻松添加前导零：
>>> format(10, '08b')
'00001010'
