[Tutor] Type Checking:

[Danny Yoo]

On Sat, 3 Mar 2001, Tim Johnson wrote:

> Consider the following code:
> # code begins
> >>> str = 'hello'
> >>> type(str)
> <type 'string'>
> >>> if type(str) == 'string':         
> ...   print "it's a string"
> ... else:
> ...   print "I don't know how to type"


(Side note: try to avoid using 'str' as a variable name: it's already the
name of the built-in str() function that converts anything to a string.  
This warning is meant to avoid potential weirdness later on; you'll
probably want to keep that str() function for a rainy day.  *grin*)


Other people have already pointed out that

    type(mystr) == types.StringType

is the traditional way of doing the type comparison.  The reason that

    type(mystr) == 'string':         

doesn't quite work is because types are things --- objects --- that need
to be compared with either other.  This might not make much sense yet;
let's make an analogy with what we already know.  In Python:

    1 == '1'

is false, even though they 'look' the same, and the reason is because
numbers are different from strings.  Likewise:

    type(mystr) == "<type 'string'>"

doesn't work either; types are things that are different from both strings
and numbers.  That's why Python has a premade collection of these type
objects in the 'types' module, to make the comparison easier and to avoid
this issue.  However, in a pinch, this will work:

    type(mystr) == type('this is a string')

because we grab the type of mystr, and grab the type of a string, and
compare the two.  This works because we're comparing between alike things.  
It's the apples and oranges argument, taken in a very literal setting.

(Does anyone find it humorous that there's even a types.TypeType object in
there?)

Good luck to you.