Shapely is a Python package for manipulation and analysis of 2D geospatial
geometries. It is based on GEOS (http://geos.refractions.net). Shapely 1.0
is not concerned with data formats or coordinate reference systems.
Responsibility for reading and writing data and projecting coordinates
is left to other packages like WorldMill and pyproj. 

WWW: http://pypi.python.org/pypi/Shapely/