Adding new methods to new-style classes dynamically

[Max Derkachev]

Good day to all.

Some time ago I'd been playing with a framework which uses dynamic
class creation havily. Say, I could do:

class A:
pass

# I method name is dynamic
meth_name = 'foo'

#method code can also be dynamic - any executable object will be good
enough
func = lambda self: self.__class__. __name__

A.__dict__[meth_name] = func
a = A()
print a.foo()

A # methods could be added/changed at runtime, without re-instantination
A.__dict__[meth_name] = lambda self: type(self)
print a.foo() <type 'instance'>
#well, try this with the new-style class
class A(object):
pass

# the new-style __dict__ is a dictproxy object
A.__dict__[meth_name] = lambda self: type(self)Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
TypeError: object does not support item assignment

Of course, I can do
A.foo = some_executable _object
But that does help when a dynamic method name is needed.
Another option is:
exec('A.%s = %s'%('foo', 'some_executabl e_option'))
But I don't like eval'ling things :)

Is there other way to add/change methods to new-style classes
dynamically?

[Michele Simionato]

Do you mean setattr?

setattr(A, meth_name, lambda self: type(self))
Michele Simionato

[John Machin]

Max Derkachev wrote:
[snip]

#well, try this with the new-style class
class A(object):
pass

# the new-style __dict__ is a dictproxy object
A.__dict__[meth_name] = lambda self: type(self)

Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
TypeError: object does not support item assignment

Of course, I can do
A.foo = some_executable _object
But that does help when a dynamic method name is needed.
Another option is:
exec('A.%s = %s'%('foo', 'some_executabl e_option'))
But I don't like eval'ling things :)

Is there other way to add/change methods to new-style classes
dynamically?

Ever considered setattr()? Not only does it appear to do the job but
also it avoids those __make__your__e yes__bleed__ double underscores.

class A(object): .... pass
.... A.__dict__['foo'] = 123 Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: object does not support item assignment setattr(A, 'foo', 123)
A.foo 123>> def bar(self): .... print 'bar bar blog ship'
.... setattr(A, 'bar', bar)
eh = A()
eh.bar() bar bar blog ship

HTH,
John

[Max Derkachev]

John Machin wrote:

A.foo

123

Oh, I've been a little dumb to forget about it :)
Thanks.

Max.

[Jack Diederich]

On Thu, May 05, 2005 at 01:35:09AM -0700, Max Derkachev wrote:

Good day to all.

Some time ago I'd been playing with a framework which uses dynamic
class creation havily. Say, I could do: <snip>
#well, try this with the new-style class
class A(object):
pass

# the new-style __dict__ is a dictproxy object
A.__dict__[meth_name] = lambda self: type(self)

Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
TypeError: object does not support item assignment
Is there other way to add/change methods to new-style classes
dynamically?

import new
dir(new) ['__builtins__', '__doc__', '__file__', '__name__', 'classobj', 'code', 'function', 'instance', 'instancemethod ', 'module'] def foo(self): .... print "FOO!" A.foo = new.instancemet hod(foo, None, A) # func, object, class
A.foo <unbound method A.foo> a = A()
a.foo <bound method A.foo of <__main__.A object at 0xb7e0b4cc>> a.foo()

FOO!

-jackdied