list vs. dict

David Eppstein eppstein at
Thu Feb 28 16:10:25 EST 2002

In article <3C7E8D47.21BE30B3 at>,
 Jeff Shannon <jeff at> wrote:

> No, it's not something that people often use.  Generally, if you want 
> dict-like behavior, you just use a dict.  The times that it's worth the 
> effort to fake the behavior with something else, are pretty unusual.  
> The speed difference between lists and dicts isn't all that significant, 
> anyhow, and which one has the advantage depends on how you're using it.  
> Python dicts are pretty amazingly nifty, really; there's no reason to be 
> shy about using them.

I agree.  I had been looking at some code where I needed two-dimensional 
arrays, which I was coding as lists of lists, and it was getting pretty 
ugly initializing the list of lists so that each list is distinct --
[[None]*x]*y doesn't work for reasons I'll leave as an exercise.

Finally, I realized I could just use a dict.  No tricky initialization, and 
the syntax for double indexing dict[x,y] is even slightly nicer than 
list_of_lists[x][y].  Unlike a list of lists, it's easy to grow the range 
of indices: just start using them.  It would be good if dict.has_key(x,y) 
worked without having to double the parentheses, but that's only a minor 
David Eppstein       UC Irvine Dept. of Information & Computer Science
eppstein at

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