Easy Q: dealing with object type

[Erik Johnson]

I quickly browsed through section 9 of the Tutorial, tried some simple
Google searches: I'm not readily seeing how to test class type. Given some
object (might be an instance of a user-created class, might be None, might
be list, might be some other "standard" type object instance), how do you
test its type?
Python 2.2.2 (#1, Mar 17 2003, 15:17:58)
[GCC 3.3 20030226 (prerelease) (SuSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

class A: .... pass
.... obj = A()
obj <__main__.A instance at 0x81778d4>

# Here, it's fairly obvious its an A-type object. A as defined in module
'__main__'.

# Some of the comparisons against "Python primitives", work as you might
expect... int <type 'int'> type(3) == int 1 ls = range(3)
ls [0, 1, 2] type(ls) <type 'list'> type(ls) == list 1 type({}) == dict 1 type(3.14) == float 1
# but this doesn't seem to extend to user-defined classes. dir(obj) ['__doc__', '__module__'] obj.__module__ '__main__' type(obj) <type 'instance'> type(obj) == A 0 type(obj) is A 0

# The following "works", but I don't want to keep a set of instances to
compare against obj2 = A()
type(obj) == type(obj2)

1

[Daniel Bickett]

On Erik Johnson wrote:

# The following "works", but I don't want to keep a set of instances to
compare against

obj2 = A()
type(obj) == type(obj2) 1

How about:

class A: pass class B: pass objA = A()
type( objA ) == type( A() ) True

then again....
objB = B()
type( objA ) == type( B() ) True

they're both of type 'instance'. So how about this:
class A: pass class B( object ): pass objA = A()
objB = B()
type( objA ) <type 'instance'> type( objB ) <class '__main__.B'> type( objB ) == B

True

I believe that achieves what you were aiming for.

--
Daniel Bickett
dbickett at gmail.com
http://heureusement.org/

[Erick]

Ah, you're running into the "old-style classes vs. new style classes".
Try subclassing from "object".

For example:

class A(object): .... pass
.... a=A()
type(a) <class '__main__.A'> type(a) == A True type(a) is A True b=A()
type(a) == type(b) True type(a) is type(b)

True
Check out the following article, it should answer your questions:
http://www.python.org/doc/2.2.3/what...00000000000000
-e

[Erick]

Ah, you're running into the "old-style classes vs. new style classes".
Try subclassing from "object".

For example:

class A(object): .... pass
.... a=A()
type(a) <class '__main__.A'> type(a) == A True type(a) is A True b=A()
type(a) == type(b) True type(a) is type(b)

True
Check out the following article, it should answer your questions:
http://www.python.org/doc/2.2.3/what...00000000000000
-e

[Erik Johnson]

"Erick" <id******@gmail.com> wrote in message
news:11**********************@g14g2000cwa.googlegr oups.com...

Ah, you're running into the "old-style classes vs. new style classes".
Try subclassing from "object".

For example:

class A(object):

That works! :) I guess I am fortunate to be running 2.2 - looks kinda ugly
prior to that.
Check out the following article, it should answer your questions:

http://www.python.org/doc/2.2.3/what...00000000000000
Thank you both for your replies! :)
-ej

[Steven Bethard]

Erik Johnson wrote:

"Erick" <id******@gmail.com> wrote in message
news:11**********************@g14g2000cwa.googlegr oups.com...

Ah, you're running into the "old-style classes vs. new style classes".
Try subclassing from "object".

For example:

>class A(object):

That works! :) I guess I am fortunate to be running 2.2 - looks kinda ugly
prior to that.

It's not horrible:

py> class A:
.... pass
....
py> class B:
.... pass
....
py> a = A()
py> a.__class__ == A
True
py> a.__class__ == B
False

Still, if you can use new-style classes, you should.

Also, you should probably Google for "duck typing". Generally, in
Python it is frowned upon to check the type of an object. There are
times when it's necessary, but if you're just starting off, my guess is
that you haven't discovered one of these times yet...

Steve