In my python environment, the Rpy and Scipy packages are already installed.

The problem I want to tackle is such:

1) A huge set of financial data are stored in a text file. Loading into Excel is not possible

2) I need to sum a certain fields and get the totals.

3) I need to show the top 10 rows based on the totals.

Which package (Scipy or Rpy) is best suited for this task?

If so, could you provide me some pointers (e.g. documentation or online example) that can help me to implement a solution?

Speed is a concern. Ideally scipy and Rpy can handle the large files when even when the files are so large that they cannot be fitted into memory

Neither Rpy or Scipy is necessary, although numpy may make it a bit easier. This problem seems ideally suited to a line-by-line parser. Simply open the file, read a row into a string, scan the row into an array (see numpy.fromstring), update your running sums and move to the next line.