Adding instance mthods

[Fernando Rodriguez]

Hi,

This sort of code works for staticmethods, but fails with instance methods.
Why does it fail? O:-)

[color=blue][color=green][color=darkred]
>>> class C (object):[/color][/color][/color]
def g(x,y):
print 'static g', x, y
g = staticmethod(g)
[color=blue][color=green][color=darkred]
>>> def h(self, x,y):[/color][/color][/color]
return x+y
[color=blue][color=green][color=darkred]
>>> C.h = h
>>> dir(C)[/color][/color][/color]
['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute __',
'__hash__', '__init__', '__module__', '__new__', '__reduce__',
'__reduce_ex__' , '__repr__', '__setattr__', '__str__', '__weakref__', 'g',
'h'][color=blue][color=green][color=darkred]
>>> C.h(3,4)[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#6 2>", line 1, in -toplevel-
C.h(3,4)
TypeError: unbound method h() must be called with C instance as first argument
(got int instance instead)

[Sean Ross]

Re: Adding instance mthods

"Fernando Rodriguez" <frr@easyjob.ne t> wrote in message
news:7k0nqvkvhf svvvubfv7iag56l 6i9n66eri@4ax.c om...[color=blue]
> Hi,
>
> This sort of code works for staticmethods, but fails with instance[/color]
methods.[color=blue]
> Why does it fail? O:-)
>
>[color=green][color=darkred]
> >>> class C (object):[/color][/color]
> def g(x,y):
> print 'static g', x, y
> g = staticmethod(g)
>[color=green][color=darkred]
> >>> def h(self, x,y):[/color][/color]
> return x+y
>[color=green][color=darkred]
> >>> C.h = h
> >>> dir(C)[/color][/color]
> ['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute __',
> '__hash__', '__init__', '__module__', '__new__', '__reduce__',
> '__reduce_ex__' , '__repr__', '__setattr__', '__str__', '__weakref__', 'g',
> 'h'][color=green][color=darkred]
> >>> C.h(3,4)[/color][/color]
>
> Traceback (most recent call last):
> File "<pyshell#6 2>", line 1, in -toplevel-
> C.h(3,4)
> TypeError: unbound method h() must be called with C instance as first[/color]
argument[color=blue]
> (got int instance instead)[/color]


Hi.
It fails because "C.h = h" adds an unbound instance method to C, not a
static method.
To use an unbound instance method, you either need to call it on an instance
of C
(e.g., c.h(x,y)) or pass an instance of C as the first parameter (e.g.,
C.h(c, x, y)).

For example:
[color=blue][color=green][color=darkred]
>>> class C: pass[/color][/color][/color]
....[color=blue][color=green][color=darkred]
>>> def f(self, x, y):[/color][/color][/color]
.... return x + y
....[color=blue][color=green][color=darkred]
>>> C.f = f
>>> C.f[/color][/color][/color]
<unbound method C.f>[color=blue][color=green][color=darkred]
>>>
>>> c = C()
>>> c.f(2,3)[/color][/color][/color]
5[color=blue][color=green][color=darkred]
>>> C.f(c, 2,3)[/color][/color][/color]
5[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]


If you want to have the same behaviour as a static method, use
staticmethod():
[color=blue][color=green][color=darkred]
>>> def g():[/color][/color][/color]
.... print "hello"
....[color=blue][color=green][color=darkred]
>>> C.g = g
>>> C.g()[/color][/color][/color]
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
TypeError: unbound method g() must be called with C instance as first
argument (got nothing instead)[color=blue][color=green][color=darkred]
>>> C.g = staticmethod(g)
>>> C.g()[/color][/color][/color]
hello[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

HTH
Sean