[Tutor] Making big 'uns into little 'uns

[Dave Angel]

On 09/06/2012 10:15 AM, Ray Jones wrote:
> On 09/06/2012 07:15 AM, Dave Angel wrote:
>> On 09/06/2012 09:56 AM, Ray Jones wrote:
>>> I have a multiple 'if' expression that I need to drastically reduce in
>>> size, both for readability and to keep errors from creeping in.
>>>
>>> For example, I would like to have the variable 'test' point to the a
>>> location 'grid[rcount-1][ccount-1]' so that everywhere I would use
>>> 'grid.....', I could replace it with 'test' How would I accomplish that?
>>>
>>> Thanks.
>>>
>>>
>> Easiest way:   switch to C++
>>
>> There is no preprocessor in Python, and no addresses.  There are some
>> places you could fake such stuff, but not the expression you have.
>>
>> If I HAD to do something like this for Python, I'd write a
>> preprocessor.  But one reason I came to Python is its elegance, and a
>> preprocessor isn't elegant.
> Well, of all the.....   a REAL programming language..... I mean, even
> Bash.... ;;))
> 
> Anyway, it was a shot. Thanks.
> 
> 

I don't know your use-case.  For that matter, I don't even know what
semantics you mean by the grid[xx][yy] expression.  For example, are
grid, rcount, and ccount globals?  Or are you constraining 'test' to
only be used in the context where they are all visible?   Or are you
defining this location as the offset within grid where rcount and ccount
happen to point to right now?  I can see maybe a dozen "reasonable"
meanings, each requiring a different sets of constructs in the language
or its preprocessor.

One thing you can do in Python, but not in any other language I've used,
is to define a class instance property.  For example, if you were
willing to use q.test instead of test, you could do something like:

class Q(object):
    @property
    def test(self):
        return grid[rcount-1][ccount-1]

That would give you readonly access to an object defined by 3 variables
that have to be visible to the Q code.  And you could make the
expression more complex if grid is defined elsewhere, for example.

Now once you do  q = Q(), you can use
    q.test  instead of the larger expression.

Lots of other possibilities in Python.  But not with exactly your
original syntax.  Using this one as is would be ugly code, as is your
original example.  So presumably you have an actual use-case where this
makes sense, other than saving typing.

-- 

DaveA