On Jun 16, 11:16 pm, "Diez B. Roggisch" <[EMAIL PROTECTED]> wrote: > méchoui schrieb: > > > > > Problem: > > > - You have tree structure (XML-like) that you don't want to create > > 100% in memory, because it just takes too long (for instance, you need > > a http request to request the information from a slow distant site). > > - But you want to be able to request data from it, such has "give me > > all nodes that are under a "//foo/bar" tree, and have a child with an > > "baz" attribute of value "zzz". > > > Question : > > > Do you have any other idea to request data from a lazily-created tree > > structure ? > > > And does it make sense to create a DOM-like structure and to use a > > generic XPath engine to request the tree ? (and does this generic > > XPath engine exist ?) > > > The idea is to have the tree structure created on the fly (we are in > > python), only when the XPath engine requests the data. Hopefully the > > XPath engine will not request all the data from the tree (if the > > request is smart enough and does not contain **, for instance). > > Generic XPath works only with a DOM(like) structure. How else would you > e.g. evaluate an expression like foo[last()]? > > So if you really need lazy evaluation, you will need to specifically > analyze the query of interest and see if it can be coded in a way that > allows to forget as much of the tree as possible, or even better not > query it. > > Diez
Yes, I need to make sure my requests are properly written so that the generic XPath engine does not need all the structure in memory. There are quite a few cases where you really don't need to load everything at all. /a/b/*/c/d is an example. But even with an example like /x/z[last()]/t, you don't need to load everything under the every /x/z nodes. You just need to check for the latest one, and make sure there is a t node under it. Anyway, if I need to make requests that need all the data... that means that the need for lazy instantiation of nodes disappears, right ? -- http://mail.python.org/mailman/listinfo/python-list
