如何检查给定的数字是否为数字？

Question

How can I check if a number is composed by a single digit?

Here is what I have tried so far:

n=5
def digit(n):
   for i in [0,1,2,3,4,5,6,7,8,9]:
       if ???
           return True
       else:
           return False

The output in this case should be `True

`

Answer 1

You can simply do

def isdigit(n):
    return n in range(10)

Answer 2

I'm not saying it's the best way to do it, but it's probably what you meant to do:

def digit(n):
    for i in [0,1,2,3,4,5,6,7,8,9]:
        if n == i:
            return True
    else:
        return False
digit(5)

Output:

True

Please pay attention that the else clause is not part of the if , but part of the for , which means that it will be executed only if the loop ended without any return or break during the iterations. You can also not use the else at all, and just return False after the loop.