试图了解int类型

Question

I'm new to Python and am trying to understand types. Specifically, can someone explain why I am getting these results?

>>> start = 1
>>> start is int
False
>>> type(start)
<class 'int'>

I ask, because I am trying to run a test in a script and can't understand why it is failing the test, and I am afraid to cast the input as an int because, if it isn't, I want to make sure it doesn't pass this test. here's the code:

def slice(self, start=0, stop=0, step=1):
    if start != 0 and start is not int:
        for item in self.data:
            if start in item:
                start = self.data.index(item)

But when I do this:

slice(1,10)

It fails the "start is not int" and drops into the for loop.

Any help, please?

Answer 1

You should do: isinstance(start, int) .

start is int checks whether start is the type int , not whether start is an instance of the type int .

>>> start = 1
>>> start is int
False
>>> isinstance(start, int)
True

Answer 2

From the Python 3 documentation:

The operators is and is not test for object identity: x is y is true if and only if x and y are the same object. x is not y yields the inverse truth value. [4]

start is 1 while int is a Python class. Here's some sample code that may help you:

>>> start = 1
>>> start is int
False
>>> start == int
False
>>> start is 1
True
>>> start == 1
True
>>> type(start) == int
True

You should use type() or isinstance() (as Simeon suggested).