Adding instance mthods

[Fernando Rodriguez]

Hi,

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

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

Traceback (most recent call last):
File "<pyshell#62>", 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]

"Fernando Rodriguez" <fr*@easyjob.net> wrote in message
news:7k********************************@4ax.com...

Hi,

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

class C (object): def g(x,y):
print 'static g', x, y
g = staticmethod(g)
def h(self, x,y): return x+y
C.h = h
dir(C) ['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute__',
'__hash__', '__init__', '__module__', '__new__', '__reduce__',
'__reduce_ex__', '__repr__', '__setattr__', '__str__', '__weakref__', 'g',
'h'] C.h(3,4)
Traceback (most recent call last):
File "<pyshell#62>", 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)

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:

class C: pass .... def f(self, x, y): .... return x + y
.... C.f = f
C.f <unbound method C.f>
c = C()
c.f(2,3) 5 C.f(c, 2,3) 5

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

HTH
Sean