On Mon, Sep 28, 2009 at 12:11 AM, Maurizio <maurizio.gran...@gmail.com> wrote:
>
> First of all, thank you for the example!
>
>>
>> I'm pretty sure it is impossible to decide whether a cells output depends on
>> the
>> value of a given variable. You could get it write some of the time by seeing
>> if the variable appears, but given the dynamic nature of Python it is
>> impossible to
>> decide in general.
>>
>
> What about the preparser? Can't we use it to recognize whether any
> variable belonging to the "live" list appear in the lines of the
> current cell? Then, it could just automatically append the "depend"
> attribute to the cell id.
Sure, one could do that using the preparser. Unfortunately that
wouldn't really work because one cell can easily depend on the
variable x without the letter x explicitly appearing anywhere in the
cell. For example, suppose I define a function:
def foo():
print x
in one cell, then put
print foo()
in another cell. The cell with "print foo()" in it depends on the
value of x, but x is not mentioned explicitly anywhere in that cell.
>
>> That said, if you were allowed to tag a cell as depending, then this is easy
>> to
>> implement. I've even made an implementation of this in the current notebook:
>>
>> http://sagenb.org/home/pub/905/
>>
>> If you try that and evaluate all the cells in order, then you'll see
>> that changing a and b
>> causes all the other dependent cells to update. You can add
>> non-dependent cells and
>> they won't update. Obviously the above is a bit cumbersome, but could
>> be made smoother
>> if it gets at what you're after.
>>
>> William
>>
>
> After all, I'd be glad to see if any interest is shown in this
> direction, since there is a reasonable amount of work around the
> notebook now. Otherwise, thank you for the discussion :)
>
> Maurizio
> >
>
--
William Stein
Associate Professor of Mathematics
University of Washington
http://wstein.org
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