SF patch #510288 by Kevin J. Butler, mod'd by Barry. This provides better auto-recognition of a Jython file vs. a CPython (or agnostic) file by looking at the #! line more closely, and inspecting the import statements in the first 20000 bytes (configurable). Specifically, (py-import-check-point-max): New variable, controlling how far into the buffer it will search for import statements. (py-jpython-packages): List of package names that are Jython-ish. (py-shell-alist): List of #! line programs and the modes associated with them. (jpython-mode-hook): Extra hook that runs when entering jpython-mode (what about Jython mode? <20k wink>). (py-choose-shell-by-shebang, py-choose-shell-by-import, py-choose-shell): New functions. (python-mode): Use py-choose-shell. (jpython-mode): New command. (py-execute-region): Don't use my previous hacky attempt at doing this, use the new py-choose-shell function. One other thing this file now does: it attempts to add the proper hooks to interpreter-mode-alist and auto-mode-alist if they aren't already there. Might help with Emacs users since that editor doesn't come with python-mode by default.