Python 如何检查变量是整数还是字符串？

How to check if a variable is an integer or a string?

提问by user2154354

I have an application that has a couple of commands. When you type a certain command, you have to type in additional info about something/someone. Now that info has to be strictly an integer or a string, depending on the situation.

我有一个包含几个命令的应用程序。当您输入某个命令时，您必须输入有关某事/某人的附加信息。现在，该信息必须严格为整数或字符串，具体取决于具体情况。

However, whatever you type into Python using raw_input() actually is a string, no matter what, so more specifically, how would I shortly and without try...except see if a variable is made of digits or characters?

但是，无论您使用 raw_input() 在 Python 中输入什么，实际上都是一个字符串，无论如何，更具体地说，我将如何在不尝试的情况下很快...除了查看变量是由数字还是字符组成？

采纳答案by Martijn Pieters

In my opinion you have two options:

在我看来，您有两种选择：

• Just try to convert it to an int, but catch the exception:

  try:
      value = int(value)
  except ValueError:
      pass  # it was a string, not an int.
  

  This is the Ask Forgiveness approach.

• Explicitly test if there are only digits in the string:

  value.isdigit()
  

  str.isdigit()returns Trueonly if all characters in the string are digits (0-9).

  The unicode/ Python 3 strtype equivalent is unicode.isdecimal()/ str.isdecimal(); only Unicode decimals can be converted to integers, as not all digits have an actual integer value (U+00B2 SUPERSCRIPT 2is a digit, but not a decimal, for example).

  This is often called the Ask Permission approach, or Look Before You Leap.

• 只需尝试将其转换为 an int，但捕获异常：

  try:
      value = int(value)
  except ValueError:
      pass  # it was a string, not an int.
  

  这就是请求宽恕的方法。

• 显式测试字符串中是否只有数字：

  value.isdigit()
  

  str.isdigit()True仅当字符串中的所有字符都是数字 ( 0- 9)时才返回。

  的unicode/ Python的3str型当量unicode.isdecimal()/ str.isdecimal(); 只有 Unicode 小数可以转换为整数，因为并非所有数字都有实际的整数值（例如，U+00B2 SUPERSCRIPT 2是数字，但不是小数）。

  这通常被称为“询问许可”方法，或“跃跃欲试”。

The latter will not detect all valid int()values, as whitespace and +and -are also allowed in int()values. The first form will happily accept ' +10 'as a number, the latter won't.

后者不会检测所有有效值int()，如空格，并且+和-也允许在int()值中。第一种形式很乐意接受' +10 '为数字，后者不会。

If your expect that the user normallywill input an integer, use the first form. It is easier (and faster) to ask for forgiveness rather than for permission in that case.

如果您希望用户通常会输入一个整数，请使用第一种形式。在这种情况下，请求宽恕比请求许可更容易（也更快）。

回答by jwodder

The isdigitmethod of the strtypereturns Trueiff the given string is nothing but one or more digits. If it's not, you know the string should be treated as just a string.

如果给定的字符串只是一个或多个数字isdigit，则该str类型的方法返回True。如果不是，您知道该字符串应该被视为一个字符串。

回答by TehTris

if you want to check what it is:

如果你想检查它是什么：

>>>isinstance(1,str)
False
>>>isinstance('stuff',str)
True
>>>isinstance(1,int)
True
>>>isinstance('stuff',int)
False

if you want to get ints from raw_input

如果你想从 raw_input 获取整数

>>>x=raw_input('enter thing:')
enter thing: 3
>>>try: x = int(x)
   except: pass

>>>isinstance(x,int)
True

回答by Marcin

Don't check. Go ahead and assume that it is the right input, and catch an exception if it isn't.

不要检查。继续并假设它是正确的输入，如果不是，则捕获异常。

intresult = None
while intresult is None:
    input = raw_input()
    try: intresult = int(input)
    except ValueError: pass

回答by Alexei Sholik

Depending on your definition of shortly, you could use one of the following options:

根据您对 short 的定义，您可以使用以下选项之一：

• try: int(your_input); except ValueError: # ...
• your_input.isdigit()
• use a regex
• use parsewhich is kind of the opposite of format

• try: int(your_input); except ValueError: # ...
• your_input.isdigit()
• 使用正则表达式
• 使用parse与format