[Pytables-users] Reading single column from table

[Julio T. <jul...@gm...>]

Hi,

I just joined this list, I am using PyTables for my project and it works
great and fast.

I am just trying to optimize some parts of the program and I noticed that
zipping the tuples to get one tuple per column takes much longer than
reading the data itself. The thing is that readWhere() returns one tuple
per row, whereas I I need one tuple per column, so I have to use the zip()
function to achieve this. Is there a way to skip this zip() operation?
Please see below:


    def quote_GetData(self, period, name, dt1, dt2):
        """Returns timedata.Quotes object.

        Arguments:
          period -- value from within infogetter.QuotePeriod
          name -- quote symbol
          dt1, dt2 -- datetime.datetime or timestamp values

        """
        t = time.time()
        node = self.quote_GetNode(period, name)
        ts1 = misc.datetime2timestamp(dt1)
        ts2 = misc.datetime2timestamp(dt2)

        L = node.readWhere( \
                   "(timestamp/1000 >= %f) & (timestamp/1000 <= %f)" % \
                   (ts1/1000, ts2/1000))
        rowNum = len(L)
        Q = timedata.Quotes()
        print "%s: took %f seconds to do everything else" % (name,
time.time()-t)

        t = time.time()
        if rowNum > 0:
            (Q.timestamp, Q.open, Q.close, Q.high, Q.low, Q.volume, \
             Q.numTrades) = zip(*L)
        print "%s: took %f seconds to ZIP" % (name, time.time()-t)
        return Q

*And the printout:*
BOVESPA.VISTA.PETR4: took 0.068788 seconds to do everything else
BOVESPA.VISTA.PETR4: took 0.379910 seconds to ZIP