My first Python program -- a lexer

[Steve Holden]

Thomas Mlynarczyk wrote:
> John Machin schrieb:
> 
>> *IF* you need to access the regex associated with a token in O(1)
>> time, a dict is indicated.
> 
> O(1) - Does that mean `mydict[mykey]` takes the same amount of time, no
> matter if mydict has 10 or 1000000000 entries? How does this magic work?
> O(log n) I would understand, but constant time?
> 
Basically it hashes the key values to locate the corresponding value.

This is a drastic simplification, but if you do a Google search for
"hash tables" you will get the basic idea. Tim Peters, among others, has
spent a lot of time optimizing dict behavior.

>> If you have *both* requirements simultaneously, then *both* list and
>> dict are indicated.
> 
> So I would have to duplicate my data and store it once in a list, once
> in a dict? Or should I decide for one way and accept that one type of
> access will not be optimal?
> 
Storing the data once in a dict and once in a list doesn't duplicate the
data, since both structures will (optimally: i.e. if you do it right)
refer to the same data objects.

Generally speaking, do what's convenient to do as a programmer, and work
on it if there are serious inadequacies.

regards
 Steve
-- 
Steve Holden        +1 571 484 6266   +1 800 494 3119
Holden Web LLC              http://www.holdenweb.com/