To date, Biopython releases have relied on the original numerical python library, Numeric (used in python with “import Numeric”). In the next release we will at last be moving to its successor, NumPy (used in python with “import numpy”).
This transition is already under way in the Biopython source code repository. For further details, or to voice your opinion or enthusiasm, please join the Biopython Mailing List(s).
Finally, for anyone interested in the background story, the SciPy project has a page describing the history of the numerical python libraries.