Overriding methods on a per instance basis

[Kunal Jamdade]

I tried to understand  overriding methods on per instance class. But i am
not getting it. Can you help me in getting the mail. Or can u suggest me at
least what should i read before reading "this topic"?

Can you explain me with one more example?

On Tue, May 16, 2017 at 9:30 AM, Nathan Ernst <nathan.ernst at gmail.com>
wrote:

> There is another way to do it, but it's not pretty, and I don't recommend
> it:
> >>> class Foo:
> ...     pass
> ...
> >>> from functools import partial
> >>> f = Foo()
> >>> def hello(self, arg):
> ...     print("hello", arg)
> ...
> >>> f.hello = partial(hello, f)
> >>> f.hello("world")
> hello world
>
> This basically relies upon binding in a closure. It's close, but not quite
> right. i.e. if you copy the instance, the function will remember the
> original and not know about the copy.
>
> On Sun, May 14, 2017 at 11:01 AM, Steve D'Aprano <
> steve+python at pearwood.info
> > wrote:
>
> > It is common to add an attribute to a class, then over-ride it in the
> > instance:
> >
> >
> > class Document:
> >     pagesize = "A4"
> >
> >     def __init__(self, pagesize):
> >         self.pagesize = pagesize
> >
> >
> > A little-known fact, not appreciated by users of less powerful OOP
> > languages: Python supports per-instance customized methods too, since
> > methods are just attributes.
> >
> >
> > py> class Parrot:
> > ...     name = "Polly"
> > ...     def speak(self):
> > ...         return "%s wants a cracker!" % self.name
> > ...
> > py> petey = Parrot()
> > py> petey.speak()
> > 'Polly wants a cracker!'
> >
> >
> > We can shadow petey's "speak" method with a callable:
> >
> > py> petey.speak = lambda: "Who's a cheeky boy then!"
> > py> petey.speak()
> > "Who's a cheeky boy then!"
> >
> >
> > Notice that using a regular function means that we cannot access "self".
> > But
> > all is not lost! We can do so by using a method object bound to the
> > instance:
> >
> > py> from types import MethodType
> > py> petey.speak = MethodType(
> > ...     lambda self: "%s is a cheeky boy!" % self.name,
> > ...     petey)
> > py> petey.speak()
> > 'Polly is a cheeky boy!'
> >
> >
> >
> >
> > This can be considered a form of the Strategy design pattern. From
> > Wikipedia:
> >
> >     ... the strategy pattern (also known as the policy pattern)
> >     is a behavioural software design pattern that enables an
> >     algorithm's behavior to be selected at runtime. The strategy
> >     pattern:
> >
> >     - defines a family of algorithms,
> >     - encapsulates each algorithm, and
> >     - makes the algorithms interchangeable within that family.
> >
> > https://en.wikipedia.org/wiki/Strategy_pattern
> >
> > the major difference being is that in the Strategy pattern there is not
> > necessarily a default implementation provided by the class:
> >
> > class Dog:
> >     pass
> >
> > rover = Dog()
> > butch = Dog()
> > laddie = Dog()
> >
> > rover.do_trick = fetch_stick
> > butch.do_trick = play_dead
> > laddie.do_trick = solve_world_hunger
> >
> >
> >
> >
> > --
> > Steve
> > Emoji: a small, fuzzy, indistinct picture used to replace a clear and
> > perfectly comprehensible word.
> >
> > --
> > https://mail.python.org/mailman/listinfo/python-list
> >
> --
> https://mail.python.org/mailman/listinfo/python-list
>