[Tutor] Test for type(object) == ???

[Steven D'Aprano]

On Fri, Feb 10, 2017 at 07:34:35PM -0600, boB Stepp wrote:
> I was playing around with type() tonight.  If I type (pun intended), I get:
> 
> py3: type(5)
> <class 'int'>
> 
> So I naively thought a test for type int should go like:
> 
> py3: type(5) == "<class 'int'>"
> False


The interactive intepreter is great, but you have to remember that what 
you see is not necessarily what you've got. What you *see* is the string 
representation of the object:

py> print
<built-in function print>

but what you've actually got is the object itself; in this case, it is 
the print function, and in your case, it is the int class.

Generally angle brackets < > mean that the text between the brackets is 
just a display form, something intended for the human reader, and not a 
programmable syntax. You then have to know (from experience) how to 
refer to the object in code.

In the case of int, there are three distinct things here:

- the class (or type) itself, a blob of memory somewhere in the 
interpreter containing various methods and attributes used for working 
with integers;

- the name the interpreter knows that class by, namely "int";

- the string representation for the human reader, "<class 'int'>".


So long as you remember the difference between the object itself, the 
name we use to talk about the object, and the way we visually display 
the object, you can't go wrong :-)

(The nation Russia is not the same as a map of Russia, which is not the 
same as the word Russia, which is not the same as the letters R u 
s s i a, or even Р о с с и ́я for that matter). 

As they say: the map is not the territory. Or in the words of Steven 
Wright, "I have a map of the United States... Actual size. It says, 
'Scale: 1 mile = 1 mile.' I spent last summer folding it."


> I finally stumbled onto the correct form:
> 
> py3: type(5) == int
> True

type(5) returns the class that we call "int". The name "int" returns 
that same class.


> So my question is why does "type(5)" result in "<class 'int'>",

No, that's just the string representation of int.

Inside the interactive interpreter, when you hit ENTER, the interpreter 
evaluates the line of code you have, generates a result, and then does 
the equivalent of:

print(repr(result))

(except that None is suppressed).


-- 
Steve