a Python person's experience with Ruby

[Bruno Desthuilliers]

MonkeeSage a écrit :
> On Dec 7, 11:08 pm, Steve Howell <showel... at yahoo.com> wrote:
> 
(snip)
>>  4) Ruby forces you to explicitly make attributes for
>> instance variables.  At first I found this clumsy, but
>> I've gotten used to it, and I actually kind of like it
>> in certain circumstances.

> 4.) Yeah, it's hard when learning ruby, especially if coming from
> languages that distinguish between methods and attributes,

which is not the case in Python

> to get used
> to thinking of "a.a" and "a.a=" as method calls and defining accessors
> for those methods  (or using one of the attr_* keywords) in the class
> body. 

Python has an equivalent support for computed attributes, using property 
or a custom descriptors. While it's a bit lower-level than Ruby, it's 
still quite easy to use and IMHO a bit more powerful.

> The equivalent python idiom is something like:
> 
> class A:
>   __a = "foo"
>   def __init__(self):
>     self.a = A.__a

WTF ???

> Which roughly translates to this in ruby:
> 
> class A
>   attr_accessor :a
>   def initialize
>     @a = "foo"
>   end
> end

The Python translation of the above Ruby snippet is actually way more 
simple:

class A(object):
   def __init__(self):
     self.a = "foo"


> Python:
> 
> 1.) I also found python's style of method referencing to be a lot more
> intuitive than using something like ruby's "m = method('foo');
> m.call('bar')" to get a reference to foo() and call it. It's alot
> cleaner to say "m = foo; m('bar')", imo. But this goes back to the
> omitting parens thing, which makes it impossible to do it that way in
> ruby.

Yeps. This is where the real and fundamental difference between Ruby and 
Python becomes evident. Both have support for transparent computed 
attributes, but the way it's implemented is totally different - in Ruby, 
by not having a call operator at all (I mean, the parens), in Python by 
having both an explicit call operator and an explicit protocol for 
computed attributes (the descriptor protocol). Not to say one is better 
than the other, but that while both languages have similar features 
(and, at first look, similar syntaxes), they really have totally 
different object models.

> Though, ruby does allow some interesting things by having it
> that way, e.g., letting you substitute a Proc object (e.g., a block or
> lambda) for a method reference transparently.

Care to give an example ? I don't have enough working experience with 
Ruby to be sure I understand what you mean here.

> 2.) I also find layout to be a nice feature. And since I've recently
> been using Haskell, it has only re-inforced that opinion. But when I
> first started using python, I got bitten by IndentationError quite
> often. And I kept wanting to type some closing symbol, heh. ;)

The nice thing with Python is that it lets you use the closing symbol 
you want, as long as you prefix it with a '#' !-)