Understanding Python Code

[subhabangalore at gmail.com]

On Thursday, June 19, 2014 12:45:49 AM UTC+5:30, Ian wrote:
> 
> 
> > The questions are,
> 
> > i) prev_f_sum = sum(f_prev[k]*a[k][st] for k in states)
> 
> > here f_prev is called,
> 
> > f_prev is assigned to  f_curr ["f_prev = f_curr"]
> 
> > f_curr[st]  is again being calculated as, ["f_curr[st] = e[st][x_i] * prev_f_sum"] which again calls "prev_f_sum"
> 
> >
> 
> > I am slightly confused which one would be first calculated and how to proceed next?
> 
> 
> 
> These things that you describe as "calls" are not calls.  f_prev and
> 
> f_curr are data structures (in this case dicts), not functions.
> 
> Accessing "f_prev[k]" does not call f_prev or in any way cause
> 
> f_prev[k] to be computed; it just looks up what value is recorded in
> 
> the f_prev dict for the key k.
> 
> 
> 
> Python is an imperative language, not declarative.  If you want to
> 
> know what order these things are calculated in, just follow the
> 
> program flow.

Thank you for the reply. But as I checked it again I found,
f_prev[k] is giving values of f_curr[st] = e[st][x_i] * prev_f_sum
which is calculated later and again uses prev_f_sum.

Regards,
Subhabrata Banerjee.