are user defined classes hashable?

[Alan G Isaac]

Are user defined classes hashable?
(The classes; *not* the instances!)

I want to use some classes as dictionary keys.
Python is not objecting,
but I'm not sure how to think about
whether this could be dangerous.
I'm inclined to guess it will be hashed by id
and this is OK.

Thanks for any insights,
Alan Isaac

 

[Nicolas Dandrimont]

Are user defined classes hashable?
(The classes; *not* the instances!)

I want to use some classes as dictionary keys.
Python is not objecting,
but I'm not sure how to think about
whether this could be dangerous.
I'm inclined to guess it will be hashed by id
and this is OK.

You can check for yourself:

In [1]: class Foo(object):
...: pass
...:

In [2]: foo = Foo()

In [3]: hash
hash

In [3]: hash(foo)
Out[3]: 15294992

In [4]: id(foo)
Out[4]: 15294992

So yes, by default, user-defined classes are hashable, by id. You can
override this behaviour by defining the __hash__ special method on
your object.

HTH,
--
Nicolas Dandrimont

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[Alan G Isaac]

You can check for yourself:

In [1]: class Foo(object):
...: pass
...:

In [2]: foo = Foo()

In [3]: hash(foo)
Out[3]: 15294992

In [4]: id(foo)
Out[4]: 15294992

Again, my question is about the class not its instances,
but still, checking as you suggest gives the same answer.

Thanks,
Alan

 

[Nicolas Dandrimont]

Again, my question is about the class not its instances,
but still, checking as you suggest gives the same answer.

That's what I get for answering before my coffee!

Cheers,
--
Nicolas Dandrimont

"Linux poses a real challenge for those with a taste for late-night
hacking (and/or conversations with God)."
(By Matt Welsh)

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[Hyuga]

That's what I get for answering before my coffee!

Regardless, Nicolas's example can be applied to the class too:

pass

11443104

class objects are just objects of type 'type'.

 

[Aahz]

Regardless, Nicolas's example can be applied to the class too:

11443104

class objects are just objects of type 'type'.

Not quite. They certainly default that way, but changing the metaclass
changes a class's type::

class M(type):
pass

class C(object):
pass

class C2(object):
__metaclass__ = M

print type(C)
print type(C2)

 

[Hyuga]

Not quite.  They certainly default that way, but changing the metaclass
changes a class's type::

class M(type):
    pass

class C(object):
    pass

class C2(object):
    __metaclass__ = M

print type(C)
print type(C2)

Well, okay, you got me there. But the OP wasn't asking about classes
with different metaclasses. And besides, type(type(C2)) is still
type