can't set attributes of built-in/extension type

[Neal Becker]

I'm working on a simple extension. Following the classic 'noddy' example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type. More precisely, I want a class
attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?

 

[7stud]

I'm working on a simple extension.  Following the classic 'noddy' example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type.  More precisely, I want a class
attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?

class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'

 

[Neal Becker]

I'm working on a simple extension.  Following the classic 'noddy'
example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type.  More precisely, I want a
class attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call
last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?

class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'

Not quite, I'm setting a class attribute, not an attribute on an instance.

 

[Steve Holden]

I'm working on a simple extension. Following the classic 'noddy'
example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type. More precisely, I want a
class attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?

class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'

Not quite, I'm setting a class attribute, not an attribute on an instance.

Quite. The problem is that extension types' attributes are determined by
the layout of the object's slots and forever fixed in the C code that
implements them: the slots can't be extended, so there's no way to add
attributes. This is an efficiency feature: it would be *extremely* slow
to look up the basic types' attributes using late-binding (it would also
change the nature of the language somewhat, making it more like Ruby or
Self).

So the reason you can't do what you want to is the same reason why you
can't add attribute to the built-in types (which are, of course, clearly
mentioned in the error message).
Traceback (most recent call last):

If you look in typeobject.c you'll find this error message occurs when
the object's type isn't a PyHeapTypeObject (in other words, if it's one
of the built-in or extension types).

regards
Steve

 

[Neal Becker]

I'm working on a simple extension. Following the classic 'noddy'
example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type. More precisely, I want a
class attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?

class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'

Not quite, I'm setting a class attribute, not an attribute on an
instance.

Quite. The problem is that extension types' attributes are determined by
the layout of the object's slots and forever fixed in the C code that
implements them: the slots can't be extended, so there's no way to add
attributes. This is an efficiency feature: it would be *extremely* slow
to look up the basic types' attributes using late-binding (it would also
change the nature of the language somewhat, making it more like Ruby or
Self).

So the reason you can't do what you want to is the same reason why you
can't add attribute to the built-in types (which are, of course, clearly
mentioned in the error message).
Traceback (most recent call last):

If you look in typeobject.c you'll find this error message occurs when
the object's type isn't a PyHeapTypeObject (in other words, if it's one
of the built-in or extension types).

regards
Steve

Thanks, but I'm a bit confused. After reading in my "Python in a Nutshell",
I found that if after calling PyReady on my type object, if I use
PyDict_SetItemString (my_type_obj.tp_dict,)

That seems to work fine (which isn't exactly what it said in the Nutshell
book, but close).

 

[Steve Holden]

7stud wrote:

I'm working on a simple extension. Following the classic 'noddy'
example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type. More precisely, I want a
class attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?
class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'
Not quite, I'm setting a class attribute, not an attribute on an
instance.

Quite. The problem is that extension types' attributes are determined by
the layout of the object's slots and forever fixed in the C code that
implements them: the slots can't be extended, so there's no way to add
attributes. This is an efficiency feature: it would be *extremely* slow
to look up the basic types' attributes using late-binding (it would also
change the nature of the language somewhat, making it more like Ruby or
Self).

So the reason you can't do what you want to is the same reason why you
can't add attribute to the built-in types (which are, of course, clearly
mentioned in the error message).

object.anyoldname = "You lose!"

Traceback (most recent call last):

If you look in typeobject.c you'll find this error message occurs when
the object's type isn't a PyHeapTypeObject (in other words, if it's one
of the built-in or extension types).

Thanks, but I'm a bit confused. After reading in my "Python in a Nutshell",
I found that if after calling PyReady on my type object, if I use
PyDict_SetItemString (my_type_obj.tp_dict,)

That seems to work fine (which isn't exactly what it said in the Nutshell
book, but close).

I'm having a little difficulty parsing that. Could we try again?

regards
Steve

 

[Neal Becker]

Neal Becker wrote:
7stud wrote:

I'm working on a simple extension. Following the classic 'noddy'
example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type. More precisely, I want
a class attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?
class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'
Not quite, I'm setting a class attribute, not an attribute on an
instance.

Quite. The problem is that extension types' attributes are determined by
the layout of the object's slots and forever fixed in the C code that
implements them: the slots can't be extended, so there's no way to add
attributes. This is an efficiency feature: it would be *extremely* slow
to look up the basic types' attributes using late-binding (it would also
change the nature of the language somewhat, making it more like Ruby or
Self).

So the reason you can't do what you want to is the same reason why you
can't add attribute to the built-in types (which are, of course, clearly
mentioned in the error message).

object.anyoldname = "You lose!"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 'object'


If you look in typeobject.c you'll find this error message occurs when
the object's type isn't a PyHeapTypeObject (in other words, if it's one
of the built-in or extension types).

Thanks, but I'm a bit confused. After reading in my "Python in a
Nutshell", I found that if after calling PyReady on my type object, if I
use PyDict_SetItemString (my_type_obj.tp_dict,)

That seems to work fine (which isn't exactly what it said in the Nutshell
book, but close).

I wanted to add an attribute to my type.
Specifically, my type object is a static cmplx_int32_scalar_obj.

After calling PyType_Ready (&cmplx_int32_scalar_obj), then I did
PyDict_SetItemString (cmplx_int32_scalar_obj.tp_dict, "dtype", (PyObject*)d1);

Now my type has the property:
cmplx_int32.dtype
dtype('cmplx_int32')

Now, I do see that I still can't set it:

cmplx_int32.dtype = 2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 'numpy.cmplx_int32'

In this case, I don't need to.

But I still don't know why I can have a python class and set class or instance
attributes as I like, but this type acts differently. What would I need to
do if I did want to allow arbitrary attributes to be set/added to my type?

 

[Steve Holden]

Steve Holden wrote:

Neal Becker wrote:
7stud wrote:

I'm working on a simple extension. Following the classic 'noddy'
example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type. More precisely, I want
a class attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?
class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'
Not quite, I'm setting a class attribute, not an attribute on an
instance.

Quite. The problem is that extension types' attributes are determined by
the layout of the object's slots and forever fixed in the C code that
implements them: the slots can't be extended, so there's no way to add
attributes. This is an efficiency feature: it would be *extremely* slow
to look up the basic types' attributes using late-binding (it would also
change the nature of the language somewhat, making it more like Ruby or
Self).

So the reason you can't do what you want to is the same reason why you
can't add attribute to the built-in types (which are, of course, clearly
mentioned in the error message).

object.anyoldname = "You lose!"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 'object'


If you look in typeobject.c you'll find this error message occurs when
the object's type isn't a PyHeapTypeObject (in other words, if it's one
of the built-in or extension types).

Thanks, but I'm a bit confused. After reading in my "Python in a
Nutshell", I found that if after calling PyReady on my type object, if I
use PyDict_SetItemString (my_type_obj.tp_dict,)

That seems to work fine (which isn't exactly what it said in the Nutshell
book, but close).

I wanted to add an attribute to my type.
Specifically, my type object is a static cmplx_int32_scalar_obj.

After calling PyType_Ready (&cmplx_int32_scalar_obj), then I did
PyDict_SetItemString (cmplx_int32_scalar_obj.tp_dict, "dtype", (PyObject*)d1);

Now my type has the property:
cmplx_int32.dtype
dtype('cmplx_int32')

Now, I do see that I still can't set it:

cmplx_int32.dtype = 2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 'numpy.cmplx_int32'

In this case, I don't need to.

But I still don't know why I can have a python class and set class or instance
attributes as I like, but this type acts differently. What would I need to
do if I did want to allow arbitrary attributes to be set/added to my type?

I believe it's because PyType_Ready(), among its many other duties,
calls mro_internal() on the type. It seems obvious that one would want
to optimize the MRO by not allowing modifications. Yet in C it is
possible, as you point out, to do so. Hmm ...

I'll let you know if I come to any conclusion - a query to python-dev
would probably get an answer, but surely someone on this list knows already?

[Left this as a draft for a while to mull it over].

After further consideration I have concluded (without further scrutiny
of the source) that it's because the method slots in C-implemented types
are pointers to C functions not to Python functions. Would this make sense?

regards
Steve

 

[Steve Holden]

Neal Becker wrote:
Steve Holden wrote:

Neal Becker wrote:
7stud wrote:

I'm working on a simple extension. Following the classic 'noddy'
example.

In [15]: cmplx_int32
Out[15]: <type 'numpy.cmplx_int32'>

Now I want to add an attribute to this type. More precisely, I want
a class attribute.

cmplx_int32.test = 0
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)

/home/nbecker/numpy/<ipython console> in <module>()

TypeError: can't set attributes of built-in/extension
type 'numpy.cmplx_int32'

What am I missing?
class Dog(object):
def __setattr__(self, attr, val):
print "TypeError: can't set attributes of built-in/extension"
print "type 'Dog.cmplx_int32'"

d = Dog()
d.test = 0

--output:--
TypeError: can't set attributes of built-in/extension
type 'Dog.cmplx_int32'
Not quite, I'm setting a class attribute, not an attribute on an
instance.

Quite. The problem is that extension types' attributes are determined by
the layout of the object's slots and forever fixed in the C code that
implements them: the slots can't be extended, so there's no way to add
attributes. This is an efficiency feature: it would be *extremely* slow
to look up the basic types' attributes using late-binding (it would also
change the nature of the language somewhat, making it more like Ruby or
Self).

So the reason you can't do what you want to is the same reason why you
can't add attribute to the built-in types (which are, of course, clearly
mentioned in the error message).

object.anyoldname = "You lose!"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 'object'


If you look in typeobject.c you'll find this error message occurs when
the object's type isn't a PyHeapTypeObject (in other words, if it's one
of the built-in or extension types).

Thanks, but I'm a bit confused. After reading in my "Python in a
Nutshell", I found that if after calling PyReady on my type object, if I
use PyDict_SetItemString (my_type_obj.tp_dict,)

That seems to work fine (which isn't exactly what it said in the Nutshell
book, but close).

I wanted to add an attribute to my type.
Specifically, my type object is a static cmplx_int32_scalar_obj.

After calling PyType_Ready (&cmplx_int32_scalar_obj), then I did
PyDict_SetItemString (cmplx_int32_scalar_obj.tp_dict, "dtype", (PyObject*)d1);

Now my type has the property:
cmplx_int32.dtype
dtype('cmplx_int32')

Now, I do see that I still can't set it:

cmplx_int32.dtype = 2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 'numpy.cmplx_int32'

In this case, I don't need to.

But I still don't know why I can have a python class and set class or instance
attributes as I like, but this type acts differently. What would I need to
do if I did want to allow arbitrary attributes to be set/added to my type?

I believe it's because PyType_Ready(), among its many other duties,
calls mro_internal() on the type. It seems obvious that one would want
to optimize the MRO by not allowing modifications. Yet in C it is
possible, as you point out, to do so. Hmm ...

I'll let you know if I come to any conclusion - a query to python-dev
would probably get an answer, but surely someone on this list knows already?

[Left this as a draft for a while to mull it over].

After further consideration I have concluded (without further scrutiny
of the source) that it's because the method slots in C-implemented types
are pointers to C functions not to Python functions. Would this make sense?

Just to close this one off, Neal wrote to python-dev and got the
following reply from Guido himself.

This is prohibited intentionally to prevent accidental fatal changes
to built-in types (fatal to parts of the code that you never though
of). Also, it is done to prevent the changes to affect different
interpreters residing in the address space, since built-in types
(unlike user-defined classes) are shared between all such
interpreters.

regards
Steve