A question on modification of a list via a function invocation

[Gregory Ewing]

Steve D'Aprano wrote:
> py> class K: # defines an object
> ...     def __init__(self, x):
> ...             self.x = x
> ...     def append(self, value):
> ...             self.x.append(value)
> ...
> py> a = []
> py> b = K(a)
> py> a is b  # these are not the same object (they're different types)
> False
> py> b.append(99)  # but modifying b modifies a
> py> a
> [99]

You didn't mutate the object bound to b there,
you mutated the one bound to b.x, which is
also bound to a.

All you've shown is that just because a method
is named "append" doesn't mean it mutates the
object it's a method of. :-)

-- 
Greg