|  | creating a similar object from an derived class | | |
| | | Scott |  |
|  Posted: Wed Sep 03, 2008 7:09 pm Post subject: creating a similar object from an derived class |  |
Let's say I have an object:
class foo():
def create_another()
return foo()
def blah():
x = self.create_another()
... do something with X
Now I create a inherited class of this object:
class bar(foo):
...
If I call bar.create_another(), it will return a foo() instead of a
bar(). This isn't what I want. I would like bar.create_another() to
create an instance for bar(). Obviously I can do this by overriding
create_another, i.e.
class bar(foo):
def create_another()
return bar()
However, is there a way for me to modify foo() so that it
automatically creates objects of the derived class, so that I don't
have to continue to redefine create_another() ?
For example, I tried the following:
def create_another()
return self.type()()
but it did not work.
Thanks,
Scott |
| |
| | | Bruno Desthuilliers | |
| | Posted: Wed Sep 03, 2008 7:09 pm Post subject: Re: creating a similar object from an derived class | |
Scott a écrit :
| Quote: | Let's say I have an object:
|
s/object/class/
| Quote: | class foo():
def create_another()
return foo()
|
class Foo(object):
def create_another(self):
return Foo()
def blah(self):
| Quote: | x = self.create_another()
... do something with X
Now I create a inherited class of this object:
class bar(foo):
|
class Bar(Foo):
| Quote: | ...
If I call bar.create_another(), it will
|
Actually, it will raise a TypeError...
| Quote: | return a foo() instead of a
bar(). This isn't what I want. I would like bar.create_another() to
create an instance for bar().
|
def create_another(self)
return type(self)()
And while you're at it, since - at least in this concrete case - you
need access to the class but not to the instance, you could make it a
classmethod:
class Foo(object):
@classmethod
def create_another(cls):
return cls()
HTH |
| |
| | | Matimus | |
| | Posted: Wed Sep 03, 2008 7:51 pm Post subject: Re: creating a similar object from an derived class | |
| |  | |
On Sep 3, 12:09 pm, Scott <smba...@gmail.com> wrote:
| Quote: | Let's say I have an object:
class foo():
def create_another()
return foo()
def blah():
x = self.create_another()
... do something with X
Now I create a inherited class of this object:
class bar(foo):
...
If I call bar.create_another(), it will return a foo() instead of a
bar(). This isn't what I want. I would like bar.create_another() to
create an instance for bar(). Obviously I can do this by overriding
create_another, i.e.
class bar(foo):
def create_another()
return bar()
However, is there a way for me to modify foo() so that it
automatically creates objects of the derived class, so that I don't
have to continue to redefine create_another() ?
For example, I tried the following:
def create_another()
return self.type()()
but it did not work.
Thanks,
Scott
|
This works:
| Quote: | class C(object):
.... @classmethod |
.... def create_another(cls):
.... return cls()
....
| Quote: | class D(C):
.... pass |
....
| Quote: | d = D()
e = d.create_another()
isinstance(e, D)
True |
Matt |
| |
| | | MRAB | |
| | Posted: Wed Sep 03, 2008 10:29 pm Post subject: Re: creating a similar object from an derived class | |
| | | |
On Sep 3, 8:09 pm, Scott <smba...@gmail.com> wrote:
| Quote: | Let's say I have an object:
class foo():
def create_another()
return foo()
def blah():
x = self.create_another()
... do something with X
Now I create a inherited class of this object:
class bar(foo):
...
If I call bar.create_another(), it will return a foo() instead of a
bar(). This isn't what I want. I would like bar.create_another() to
create an instance for bar(). Obviously I can do this by overriding
create_another, i.e.
class bar(foo):
def create_another()
return bar()
However, is there a way for me to modify foo() so that it
automatically creates objects of the derived class, so that I don't
have to continue to redefine create_another() ?
For example, I tried the following:
def create_another()
return self.type()()
but it did not work.
If you want a foo object to be able to create another foo object and a |
bar object to be able to create another bar object then you could do
this:
class foo():
def create_another(self):
return self.__class__()
class bar(foo):
pass |
| |
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