curly-brace-aphobic?

[Mark Pilgrim]

In article <mailman.980870616.378.python-list at python.org>,
  D-Man <dsh8290 at rit.edu> wrote:
> | An essential difference is the fact that lists are ordered, but dicts aren't.
>
> Suppose I use a dict with integers as keys.  How is this different from a list?
>
> dict = { 1:"one" , 2:"two" , 3:"three" }
> list = [   "one" ,   "two" ,   "three" ]
>
> for i in len( list ) :
>       print list[i]
>
> for i in len( dict ) :
>       print dict[i]
>
> In this case, they are identical!

First, "for i in len(dict): print dict[i]" will give you a "loop over
non-sequence" error, because len returns an integer, and for requires a
sequence.  You need "for i in dict.keys(): print dict[i]".

Second, "for i in dict.keys(): print dict[i]" is not the same as "for i in
list: print list[i]" because dictionaries are unordered.  I'm not really
talking in circles here (I'm talking in sequences... no, never mind).  Just
because you defined dict in a particular order doesn't mean that the keys
stay in that order.  For instance, on my machine, just now, I did "for i in
dict.keys(): print dict[i]" and got the values in the reverse order from how
I defined them ("three two one").

See http://diveintopython.org/odbchelper_dict.html for more on dictionaries,
including a step-by-step example that illustrates this point.

-M
--
You're smart; why haven't you learned Python yet?  http://diveintopython.org/


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