[Tutor] Tutor] Careful Dictionary Building

[Kent Johnson]

doug shawhan wrote:

>     To help performance a bit, don't call dict.keys() on every iteration,
>     since you're invoking a function.
> 
>     dict = {}
>     allKeys =dict.Keys

Should be dict.keys()

>     for record in list
>       if record[0] in allKeys:
>           dict[ record[0] .append( record ) ]

Should be
   dict[record[0]].append(record)

>       else:
>           dict[ record[0] ] = [record]
>           allKeys = dict.Keys()                    # this function is
>     only invoked some of the time, not on every iteration

So you only create the list of keys when it changes; that may speed up 
the loop, depending on how many duplicates there are. But there are two 
big problems with the original program - it creates a new list of keys 
each time through the loop, and it searches for a key in the list 
instead of looking it up directly in the dict. Your change may cut down 
on the number of times the key list is created but it will not improve 
the search time at all.

In other words, you are making modest improvements to a broken 
algorithm; a better fix is to use a better algorithm.

Kent