From: Charles Comstock <cc1@...>
Date: 2004-04-06T02:59:24+09:00
Subject: Re: deciding between ruby and python

Vadim Nasardinov wrote:

> On Monday 05 April 2004 11:08, Gavin Sinclair wrote:
> 
>>And there is an insurmountable limitation (I think):
> 
> .
> 
>>    chars = words = lines = 0
>>    str.each do |line|
>>      chars += line.chomp.length
>>      words += line.split
>>      lines += 1
>>    end
> 
> .
> 
>>I don't believe [Python] can carry outside state into its
>>"substitute for blocks".
> 
> 
> Feature-by-feature comparisons are useful insofar as they help you
> understand differences and similarities between the two languages
> being compared.  Consider English and German, for example.  The former
> has an "insurmountable" limitation of not having explicit case
> markings for the nominative, genitive, accusative, and dative cases
> the way German does.
> 
> Now, this may be a useful thing to know, but it's useless as far as
> comparing the overall expressiveness, naturalness, and ease of use of
> these two languages.
> 
> As Jim Weirich already pointed out in ruby-talk 96368, closures are a
> poor man's objects.  One way of making a function carry state in
> Python is to implement it as a callable object:
> 
>     $ cat poor_mans_closure.py 
>     #!/usr/bin/python
> 
>     class Foo:
>         "A poor man's closure"
> 
>         def __init__(self, state):
>             self.__call__ = self._call
>             self.state = state
> 
>         def _call(self, x, y):
>             return x * self.state + y
> 
> 
>     foo1 = Foo(1)
>     foo2 = Foo(42)
> 
>     print foo1(2,3)
>     print foo2(2,3)
> 
>     $ ./poor_mans_closure.py 
>     5
>     87
> 

Yea but that doesn't give you the guarenteed cleanup that the yield 
syntax allows.  In c++ this would be accomplished by using a guarded 
object that would destruct when the scope was exited, there is no 
comparable operation in java, without explictely declaring a wrapping 
try / catch / finally.  In C# V2.0 it is possible because of the 
existance of yield.  It is not possible in C# 1.0.  It is possible in 
ruby ala:

def setup_and_teardown
	#code which must execute before code block a and b
	yield
	#code which must execute after code block a and b
end

setup_and_teardown() do
	# operation a) which may fail but we want setup and cleanup code
	# guarenteed
end

setup_and_teardown() do
	# operation b) which may fail but we want setup and cleanup code
	# guarenteed
end

Is there any sort of similar guarded block equivalent in python while 
still allowing multiple blocks to be called and not requiring a complex 
dispatcher routine?

Charles Comstock