Using += in a loop

[Yigal Duppen]

> I am using the following code structure in some very long (10's of
> thousands of iterations) loops.
> Is there a more efficient way that doesn't use +=?

> Would s5 = '%s,"%s"' % (s5,x[1]) be better?
> 
> t = ()
> s5 = ''
> for i in range(0,5):
>   q = breaks[brk][i]
>   x = mkup(cost*q,list*q)
>   if x[0]: t+=(x[0]/q,)
>   else: t+=(0,)
>   if x[1]: s5+=',"'+x[1]+'"'
>   else: s5+=',"-"'
> t += (0,0)
> s5 += ',"-","-"'

Without exactly understanding what it does, here are some tips:

1) make t a list; this allows you to use 'append'. This is much faster since 
append works on an existing list. <tuple> += <tuple> creates a new tuple 
every time. <list> += <list> is quite efficient as well

2) make s a list as well, append all the strings you need, and join them in 
the end.


Something like this should be faster:

t_list = []
s5_list = []
for i in range(0, 5):
        q = breaks[break][i]
        x = mkup(cost * q, list * q)
        if x[0]:
                t_list.append(x[0]/q)
        else:
                t_list.append(0)
        
        if x[1]:
                s5_list += [ ',"' , x[1] , '"']
        else:
                s5_list.append(',"-"')
t_list += (0, 0)
s5_list.append(',"-","-"')

# and convert both lists to the desired types
t = tuple(t_list)
s5 = "".join(s5_list)


No clue how much faster; that's what profile is for.

YDD
-- 
.sigmentation fault