What exactly are bound methods?

[Kylotan]

Although I see lots of references to them in various documentation, I
can't find a decent explanation of exactly what they are. I'm guessing
that it's a reference to a method that remembers which object it came
from, and that when it's called, it passes that object as the first
parameter (which would conventionally be 'self'). Is this correct?

--
Ben Sizer

[Erik Max Francis]

Kylotan wrote:

Although I see lots of references to them in various documentation, I
can't find a decent explanation of exactly what they are. I'm guessing
that it's a reference to a method that remembers which object it came
from, and that when it's called, it passes that object as the first
parameter (which would conventionally be 'self'). Is this correct?

Yep:

class C: .... def f(self, x):
.... print x
.... c = C() # c is an instance of C
C <class __main__.C at 0x402e141c> C.f # the unbound method <unbound method C.f> c.f # the bound method <bound method C.f of <__main__.C instance at 0x402e4c8c>> C.f(c, 1) # invoking unbound methods requires passing the instance 1 c.f(1) # bound methods already contain the instance

1
--
Erik Max Francis && ma*@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \
\__/ There are defeats more triumphant than victories.
-- Montaigne

[Skip Montanaro]

Ben> Although I see lots of references to them in various documentation,
Ben> I can't find a decent explanation of exactly what they are. I'm
Ben> guessing that it's a reference to a method that remembers which
Ben> object it came from, and that when it's called, it passes that
Ben> object as the first parameter (which would conventionally be
Ben> 'self'). Is this correct?

When you define a class like so:

class foo:
def bar(self):
pass

foo.bar is an unbound method. Binding the method associates it with a
particular instance. You can think of a bound method as currying the
instance object with the unbound method. For info on currying, check the
Python Cookbook:

http://aspn.activestate.com/ASPN/Coo...n/Recipe/52549

Skip

[Michele Simionato]

ky*****@hotmail .com (Kylotan) wrote in message news:<15******* *************** **@posting.goog le.com>...

Although I see lots of references to them in various documentation, I
can't find a decent explanation of exactly what they are. I'm guessing
that it's a reference to a method that remembers which object it came
from, and that when it's called, it passes that object as the first
parameter (which would conventionally be 'self'). Is this correct?

If you really want to learn the difference between functions, methods
and bound methods, you must learn descriptors:

http://users.rcn.com/python/download/Descriptor.htm

Warning: the study of descriptors may cause your head to explode ...

def f(self): pass .... class C(object): pass .... c=C()
f.__get__(c,C) <bound method C.f of <__main__.C object at 0x017716D0>> f.__get__(None, C) <unbound method C.f>