introspection inquiry

[mirandacascade@yahoo.com]

Where in the language would one find the intropsection capability to
answer the question: what class am I in?

Example:

class ExistentialCris is:
def __init__(self, text):
self.spam = text
print 'In the constructor of the %s class' % <whatever>

When the constructor method is invoked, would like to see the following
message:

In the constructor of the ExistentialCris is class

and I would like to be able to do it without substituting the literal
string 'ExistentialCri sis' for <whatever>.

My question is this: what can be substituted for <whatever> that will
make the example above work?

[Robin Becker]

Re: introspection inquiry

mirandacascade@ yahoo.com wrote:
....[color=blue]
>
> My question is this: what can be substituted for <whatever> that will
> make the example above work?
>[/color]

self.__class__. __name__
--
Robin Becker

[Michael Hoffman]

Re: introspection inquiry

Robin Becker wrote:[color=blue]
> self.__class__. __name__[/color]

Unless I misunderstood the question, that won't work. That will
give you the name of the class the object is an instance is of.
I think he wants the name of the class the method was defined in.

Here's a way to do that using metaclasses and Python's magic
double-underscore attribute-mangling feature:

"""
class SelfKnowledge(t ype):
def __init__(cls, name, bases, dict):
setattr(cls, "_%s__%s" % (name, "class_name "), name)
type.__init__(c ls, name, bases, dict)

class Nietzsche(objec t):
__metaclass__ = SelfKnowledge

def __init__(self, text):
self.spam = text
print "In the constructor of the %s class" % self.__class_na me

class Kierkegaard(Nie tzsche):
def __init__(self, text):
print "Now in the constructor of %s" % self.__class_na me
Nietzsche.__ini t__(self, text)

Nietzsche("Thus Spake Zarathustra")
print

Kierkegaard("Fe ar and Trembling")
"""

$ python test1.py
In the constructor of the Nietzsche class

Now in the constructor of Kierkegaard
In the constructor of the Nietzsche class
--
Michael Hoffman

[Diez B. Roggisch]

Re: introspection inquiry

> Unless I misunderstood the question, that won't work. That will[color=blue]
> give you the name of the class the object is an instance is of.
> I think he wants the name of the class the method was defined in.[/color]

Where is the difference? The method is defined in a class - and an instance
is created from that class.

This works as expected:

class ExistentialCris is:
def __init__(self, text):
self.spam = text
print 'In the constructor of the %s class' % self.__class__. __name__


ExistentialCris is("egal")


--
Regards,

Diez B. Roggisch

[John Roth]

Re: introspection inquiry


"Michael Hoffman" <cam.ac.uk@mh39 1.invalid> wrote in message
news:cvaaae$77q $1@gemini.csx.c am.ac.uk...[color=blue]
> Robin Becker wrote:[color=green]
>> self.__class__. __name__[/color]
>
> Unless I misunderstood the question, that won't work. That will
> give you the name of the class the object is an instance is of.
> I think he wants the name of the class the method was defined in.[/color]

If that's the case, then the inspect module should give
the tools to do it without a great deal of angst. Unfortunately,
it doesn't give you the class that defined the method, just
the class that invoked it.

John Roth

[Michael Hoffman]

Re: introspection inquiry

Diez B. Roggisch wrote:[color=blue]
>[Michael Hoffman]:[color=green]
>>Unless I misunderstood the question, that won't work. That will
>>give you the name of the class the object is an instance is of.
>>I think he wants the name of the class the method was defined in.[/color]
>
> Where is the difference? The method is defined in a class - and an instance
> is created from that class.
>
> This works as expected:
>
> class ExistentialCris is:
> def __init__(self, text):
> self.spam = text
> print 'In the constructor of the %s class' % self.__class__. __name__
>
>
> ExistentialCris is("egal")[/color]

Yes, but this doesn't work if you have a subclass:

"""
class ExistentialCris isSubclass(Exis tentialCrisis):
def __init__(self, text):
print "New constructor"
ExistentialCris is.__init__(sel f, text)

ExistentialCris isSubclass("who a")
"""

gives you:

New constructor
In the constructor of the ExistentialCris isSubclass class

But the second line is *not* in the constructor of
ExistentialCris isSubclass, it is in the constructor of ExistentialCris is.

while I read the original post as saying that he wanted
"ExistentialCri sis" there instead. Indeed this example

--
Michael Hoffman

[Michael Hoffman]

Re: introspection inquiry

John Roth wrote:
[color=blue]
> If that's the case, then the inspect module should give
> the tools to do it without a great deal of angst. Unfortunately,
> it doesn't give you the class that defined the method, just
> the class that invoked it.[/color]

Are you saying that the inspect module *should* give you the
tools to do it but does not?
--
Michael Hoffman

[Robin Becker]

Re: introspection inquiry

Michael Hoffman wrote:[color=blue]
> Robin Becker wrote:
>[color=green]
>> self.__class__. __name__[/color]
>
>
> Unless I misunderstood the question, that won't work. That will
> give you the name of the class the object is an instance is of.
> I think he wants the name of the class the method was defined in.
>
> Here's a way to do that using metaclasses and Python's magic
> double-underscore attribute-mangling feature:
>
> """
> class SelfKnowledge(t ype):
> def __init__(cls, name, bases, dict):
> setattr(cls, "_%s__%s" % (name, "class_name "), name)
> type.__init__(c ls, name, bases, dict)
>
> class Nietzsche(objec t):
> __metaclass__ = SelfKnowledge
>
> def __init__(self, text):
> self.spam = text
> print "In the constructor of the %s class" % self.__class_na me
>
> class Kierkegaard(Nie tzsche):
> def __init__(self, text):
> print "Now in the constructor of %s" % self.__class_na me
> Nietzsche.__ini t__(self, text)
>
> Nietzsche("Thus Spake Zarathustra")
> print
>
> Kierkegaard("Fe ar and Trembling")
> """
>
> $ python test1.py
> In the constructor of the Nietzsche class
>
> Now in the constructor of Kierkegaard
> In the constructor of the Nietzsche class[/color]

I guess if you're right something along the lines of
import inspect
class A:
_class_name=ins pect.currentfra me().f_code.co_ name
def __init__(self,t ext,_defining_c lass_name=_clas s_name):
print 'text=',text,'_ defining_class_ name=',_definin g_class_name

class B(A):
pass
b=B('aaa')

==>text= aaa _defining_class _name= A


could work as well, but if we only need the local name why not just
insert directly.
--
Robin Becker

[Michael Hoffman]

Re: introspection inquiry

Robin Becker wrote:[color=blue]
> import inspect
> class A:
> _class_name=ins pect.currentfra me().f_code.co_ name
> def __init__(self,t ext,_defining_c lass_name=_clas s_name):
> print 'text=',text,'_ defining_class_ name=',_definin g_class_name
>
> class B(A):
> pass
> b=B('aaa')[/color]

That won't work, if you, say, wanted to print out the name of the
class the constructor was defined in for a whole chain of
constructors. Which is about the only case I can think of where
this would be useful.
[color=blue]
> could work as well, but if we only need the local name why not just
> insert directly.[/color]

To be honest, that is what I have done every time I have needed
something like this.

I've only used metaclasses in production code once and I still debate
whether that case is a good idea or not.
--
Michael Hoffman