On Jan 3, 2:58 pm, Lie Ryan <lie.1...@gmail.com> wrote: > On 1/3/2010 10:27 PM, vsoler wrote: > > > 1) what are, in your opinion, the basic elements of the Cell class? > > The "user-entered formula" and "effective value". A Cell containing a > formula "abc" has a value of "abc"; a cell containing the formula "=1+5" > has a value of "6". You could use the 'property' decorator for the > "effective value" attribute. > > > 2) Do I need a parser to evaluate the formulas like 3*A1+A2 ? Can you > > recommend one library that already contains one? > > Yes you do. PyParsing, regex, write your own parser; choose your own > poison depending on the expected complexity of the formulaes. > > > 3) Do I need a tree data structure to represent my data? > > There are two main options for your "primary data structure": > - table (2x2 list) -- if you expect most of your cells to be filled, > this is simple, but uses lots of memory > - sparse table (list/dicts of cells) -- if you have a large table that > is mostly empty cells > > The Dependency Tree is the "side data structure"; a "Cell" is a "Node"; > a Cell's "dependencies" is the Node's "children"; a Cell's "dependant" > is the Node's "parent". Cells maintains a list of dependencies (or > dynamically generates them when requested) by analyzing the "formula" > attribute for references to other cells. > > PS: Strictly speaking, this "side data structure" is not a "Tree" as > there are multiple root nodes. I think it's called "Directed Acyclic > Graph". However, it's true that, given a cell as a root, the cell's > dependencies is a proper tree. > > > would the > > tree be an attribute of the class instance? > > you could use 'property' decorator and make the dependency tree a > "computed attribute" of the cell; many people recommended against a > 'property' that is heavy to compute though and calculating dependencies > may be quite heavy depending on the complexity of the spreadsheet. > > > I imagine a lot can be said on these questions. What I am looking for > > is some hints that help me get out of where I am now. > > > Any help is highly appreciated. > > > Vicente Soler > >
As well as what Steven & Lie have mentioned, maybe you could get inspiration from http://pyspread.sourceforge.net/ Although I've not looked at it, my gut feeling is the author would've had to address these issues (take that as a disclaimer of some sort :) ) >From not having to had a need for this sort of thing, I'd probably go for a sparse representation as a graph. But again, depends why you're segmenting the "spreadsheet" from "need to tell dependencies". Jon. -- http://mail.python.org/mailman/listinfo/python-list
