On Jun 7, 8:24 am, rusi <rustompm...@gmail.com> wrote:
> On Jun 7, 8:14 am, Mark Janssen <dreamingforw...@gmail.com> wrote:
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> > >> I am aware of what it means, but Python doesn't really have it (although
> > >> it may evolve to it with annotations).
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> > > No polymorphism huh?
>
> > > py> len([1, 2, 3]) # len works on lists
> > > 3
> > > py> len((1, 2)) # and on tuples
> > > 2
> > > py> len({}) # and on dicts
> > > 0
> > > py> len('I pity the fool') # and on strings
> > > 15
> > > py> len(b'\x23') # and on bytes
> > > 1
> > > py> len(set(range(2))) # and on sets
> > > 2
> > > py> len(frozenset(range(4))) # and on frozensets
> > > 4
> > > py> len(range(1000)) # and on range objects
> > > 1000
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> > Okay, wow, it looks like we need to define some new computer science
> > terms here.
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> Fairly definitive terms have existed since
> 1985:http://lucacardelli.name/Papers/OnUnderstanding.A4.pdf
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> > You are making an "outside view of a function" (until a better term is
> > found). So that give you one possible view of polymorphism. However,
> > *within* a class that I would write, you would not see polymorphism
> > like you have in C++, where it is within the *function closure*
> > itself. Instead you would see many if/then combinations to define
> > the behavior given several input types. I would call this simulated
> > polymorphism.
>
> Cardelli and Wegner cited above call this ad-hoc polymorphism.
> What you are calling polymorphism, they call universal polymorphism.
>
> See sect 1.3 for a summary diagram
I should have added that python has the universal polymorphism that
you want:
$ python
Python 2.7.5 (default, May 20 2013, 13:49:25)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> len([1,2])
2
>>> len([[1,2]])
1
>>> len([[[1,2]],[[3]],[[4,5]]])
3
>>>
The main thing to note about universal -> parametric polymorphism is
that one definition works for an infinite set of types, without any
extra code(ing)
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