method or function? why explicit self

binding_methods.py

class A(object):
    # method
    def foo(self, x):
        print self, x

# function -- defined after A is closed.
def bar(self, y):
    print self, y

A.bar = bar

a = A()

print "class:", A
print "A.foo:", A.foo
print "bar:", bar
print "A.bar:", A.bar
print "a.foo:", a.foo
print "a.bar:", a.bar

a.foo("alpha")
a.bar("bravo")

bar("octopus", "bacon")

#
# extra credit:
#

# it doesn't exactly work that way in reverse:
foo = A.foo
print foo
try:
    foo("llama", "hummus")
except TypeError, err:
    print err

# but you can do it:
foo = A.foo.im_func
print foo
foo("marmot", "tahini")

extra credit, continued:

assert not (a.foo is A.foo)
assert A.foo.im_func is a.foo.im_func