My first Python program -- a lexer

[Arnaud Delobelle]

Thomas Mlynarczyk <thomas at mlynarczyk-webdesign.de> writes:

> 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?

As I understand it, in theory it's not O(1) - I guess it's O(n).  But
for any non-cunningly crafted data it's as if it was O(1).

Dictionaries are implemented as hashtables, not as trees.

>> 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?

Depends what you want to do!

-- 
Arnaud