This is needed because some Python extensions require strict versioned depends on python-numpy, and using this helper script is the easiest and most consistent way to get them.
The helper script uses the information stored in /usr/share/numpy/versions, and the architecture type of the package, to generate the Depends information; for a detailed description of how the dependencies are generate, please refer to /usr/share/doc/python-numpy/README.DebianMaints .
This program is not a part of debhelper (and it's provided by python-numpy).