Adding method to a class on the fly

[John Henry]

Hi list,

I have a need to create class methods on the fly. For example, if I
do:

class Dummy:
def __init__(self):
exec '''def method_dynamic( self):\n\tretur n
self.method_sta tic("it's me")'''
return

def method_static(s elf, text):
print text
return

I like that to be the same as:

class Dummy:
def __init__(self):
return

def method_dynamic( self):
return self.method_sta tic("it's me")

def method_static(s elf, text):
print text
return

so that I can do:

dum=Dummy.metho d_dynamic()

and see "it's me" printed.

Can that be done?

Thanks,

[John Henry]

Found a message on the web that says I need to use setattr to add the
method to the class at run time. But how do I do that?

Regards,

On Jun 22, 12:02 pm, John Henry <john106he...@h otmail.comwrote :

Hi list,

I have a need to create class methods on the fly. For example, if I
do:

class Dummy:
def __init__(self):
exec '''def method_dynamic( self):\n\tretur n
self.method_sta tic("it's me")'''
return

def method_static(s elf, text):
print text
return

I like that to be the same as:

class Dummy:
def __init__(self):
return

def method_dynamic( self):
return self.method_sta tic("it's me")

def method_static(s elf, text):
print text
return

so that I can do:

dum=Dummy.metho d_dynamic()

and see "it's me" printed.

Can that be done?

Thanks,

[askel]

On Jun 22, 3:02 pm, John Henry <john106he...@h otmail.comwrote :

Hi list,

I have a need to create class methods on the fly. For example, if I
do:

class Dummy:
def __init__(self):
exec '''def method_dynamic( self):\n\tretur n
self.method_sta tic("it's me")'''
return

def method_static(s elf, text):
print text
return

I like that to be the same as:

class Dummy:
def __init__(self):
return

def method_dynamic( self):
return self.method_sta tic("it's me")

def method_static(s elf, text):
print text
return

so that I can do:

dum=Dummy.metho d_dynamic()

and see "it's me" printed.

Can that be done?

Thanks,

class Dummy:
def method(self, arg):
print arg

def method2(self, arg):
self.method(arg )

Dummy.method2 = method2
Dummy.method2(' Hello, world!')

[7stud]

On Jun 22, 2:24 pm, askel <dummy...@mail. ruwrote:

class Dummy:
def method(self, arg):
print arg

def method2(self, arg):
self.method(arg )

Dummy.method2 = method2
Dummy.method2(' Hello, world!')

Traceback (most recent call last):
File "test1.py", line 8, in ?
Dummy.method2(' Hello, world!')
TypeError: unbound method method2() must be called with Dummy instance
as first argument (got str instance
instead)

>I like that to be the same as:

class Dummy:
def __init__(self):
return

def method_dynamic( self):
return self.method_sta tic("it's me")

def method_static(s elf, text):
print text
return
so that I can do:

dum=Dummy.meth od_dynamic()

and see "it's me" printed.

When are you able to see that?

[askel]

On Jun 22, 5:17 pm, 7stud <bbxx789_0...@y ahoo.comwrote:

On Jun 22, 2:24 pm, askel <dummy...@mail. ruwrote:

class Dummy:
def method(self, arg):
print arg

def method2(self, arg):
self.method(arg )

Dummy.method2 = method2
Dummy.method2(' Hello, world!')

Traceback (most recent call last):
File "test1.py", line 8, in ?
Dummy.method2(' Hello, world!')
TypeError: unbound method method2() must be called with Dummy instance
as first argument (got str instance
instead)

I like that to be the same as:

class Dummy:
def __init__(self):
return

def method_dynamic( self):
return self.method_sta tic("it's me")

def method_static(s elf, text):
print text
return

so that I can do:

dum=Dummy.metho d_dynamic()

and see "it's me" printed.

When are you able to see that?

sorry, of course last line should be:
Dummy().method2 ('Hello, world!')

[7stud]

On Jun 22, 3:23 pm, askel <dummy...@mail. ruwrote:

sorry, of course last line should be:
Dummy().method2 ('Hello, world!')

...which doesn't meet the op's requirements.

[askel]

On Jun 22, 5:17 pm, 7stud <bbxx789_0...@y ahoo.comwrote:

On Jun 22, 2:24 pm, askel <dummy...@mail. ruwrote:

class Dummy:
def method(self, arg):
print arg

def method2(self, arg):
self.method(arg )

Dummy.method2 = method2
Dummy.method2(' Hello, world!')

Traceback (most recent call last):
File "test1.py", line 8, in ?
Dummy.method2(' Hello, world!')
TypeError: unbound method method2() must be called with Dummy instance
as first argument (got str instance
instead)

I like that to be the same as:

class Dummy:
def __init__(self):
return

def method_dynamic( self):
return self.method_sta tic("it's me")

def method_static(s elf, text):
print text
return

so that I can do:

dum=Dummy.metho d_dynamic()

and see "it's me" printed.

When are you able to see that?

there is no way to call instance method from static one. but in your
case you can make something like:

class Dummy:
@staticmethod
def method(arg):
print arg

def method2(arg):
Dummy.method(ar g)

Dummy.method2 = staticmethod(me thod2)
Dummy.method2(' Hello, world!')

- OR -

def method2(cls, arg):
cls.method(arg)

Dummy.method2 = classmethod(met hod2)
Dummy.method2(' Hello, world!')

[John Henry]

On Jun 22, 2:28 pm, askel <dummy...@mail. ruwrote:

On Jun 22, 5:17 pm, 7stud <bbxx789_0...@y ahoo.comwrote:

On Jun 22, 2:24 pm, askel <dummy...@mail. ruwrote:

class Dummy:
def method(self, arg):
print arg

def method2(self, arg):
self.method(arg )

Dummy.method2 = method2
Dummy.method2(' Hello, world!')

Traceback (most recent call last):
File "test1.py", line 8, in ?
Dummy.method2(' Hello, world!')
TypeError: unbound method method2() must be called with Dummy instance
as first argument (got str instance
instead)

>I like that to be the same as:

>class Dummy:
def __init__(self):
return

def method_dynamic( self):
return self.method_sta tic("it's me")

def method_static(s elf, text):
print text
return

>so that I can do:

>dum=Dummy.meth od_dynamic()

>and see "it's me" printed.

When are you able to see that?

there is no way to call instance method from static one. but in your
case you can make something like:

class Dummy:
@staticmethod
def method(arg):
print arg

def method2(arg):
Dummy.method(ar g)

Dummy.method2 = staticmethod(me thod2)
Dummy.method2(' Hello, world!')

- OR -

def method2(cls, arg):
cls.method(arg)

Dummy.method2 = classmethod(met hod2)
Dummy.method2(' Hello, world!')

Thanks for the response.

The above doesn't exactly do I what need. I was looking for a way to
add method to a class at run time.

What does work, is to define an entire sub-class at run time. Like:

class DummyParent:
def __init__(self):
return

def method_static(s elf, text):
print text
return

text = "class Dummy(DummyPare nt):"
text += "\n\t" + "def __init(self):"
text += "\n\t" + "\tDummyParent. __init__(self)"
text += "\n\t" + "def method_dynamic( self):"
text += "\n\t" + "\tself.method_ static(\"it's me\")"

exec text

dum=Dummy().met hod_dynamic()
Thanks again.

[attn.steven.kuo]

On Jun 22, 2:44 pm, John Henry <john106he...@h otmail.comwrote :

On Jun 22, 2:28 pm, askel <dummy...@mail. ruwrote:

(snipped)

>
The above doesn't exactly do I what need. I was looking for a way to
add method to a class at run time.

I'm not sure what you mean by this. Bind an attribute -- a method --
to class Dummy if and only if an instance of this class is created?

What does work, is to define an entire sub-class at run time. Like:

class DummyParent:
def __init__(self):
return

def method_static(s elf, text):
print text
return

text = "class Dummy(DummyPare nt):"
text += "\n\t" + "def __init(self):"
text += "\n\t" + "\tDummyParent. __init__(self)"
text += "\n\t" + "def method_dynamic( self):"
text += "\n\t" + "\tself.method_ static(\"it's me\")"

exec text

dum=Dummy().met hod_dynamic()

Thanks again.

I tend to avoid exec if possible. Also, you
seem to be a bit inexact with regard to the
term "static".
class Dummy(object):
def __init__(self):
new_method_name = 'method_dynamic '
try:
getattr(Dummy, new_method_name )
except AttributeError:
print "Creating an instance method..."
def newf(self):
"""Somethin g Descriptive Here"""
return self.method_sta tic("it's me")
newf.__name__ = new_method_name
setattr(Dummy, new_method_name , newf)
def method_static(s elf, text):
"""I hate this name. Do not confuse this with a staticmethod;
what you probably meant was that this is an attribute (a
method)
bound within the class body as opposed to elsewhere"""
print text
return # is this necessary?

d1 = Dummy()
d1.method_dynam ic()
d2 = Dummy()
d2.method_dynam ic()
print d1.method_dynam ic.im_func.__na me__
print d1.method_dynam ic.im_func.__di ct__
print d1.method_dynam ic.im_func.__do c__
print d1.method_dynam ic.im_func.__mo dule__
print d1.method_dynam ic.im_self

--
Hope this helps,
Steven

[James Stroud]

7stud wrote:

On Jun 22, 3:23 pm, askel <dummy...@mail. ruwrote:

>>sorry, of course last line should be:
Dummy().metho d2('Hello, world!')

..which doesn't meet the op's requirements.

Which were contradictory.