(defun stolfi-python-find-module-and-proc-def (arg)
  "Expects to be called when the point is within or adjacent to 
a function call of the form {modproc} consisting of one or more 
letters, digits, periods (\".\"), and underscores (\"_\").  
  If {modproc} has at least 
one period, splits it into \"{module}.{proc}\" at the last period 
and searches for the file \"{module}.py\" in 
the current directory or some near ancestor
thereof, with each period in {module} replaced by a slash (\"/\"). If it finds such a file, visits it, otherwise gives
an error message. If there are no periods in {modproc}, uses
the current buffer instead, and takes {proc} to be {modproc}.  
  Either way, searches in that buffer for the presumed definition
of {proc}. 
  With a prefix arg, uses the current window, else an alternate window. [stolfi]"
  (interactive "P")
  (let*
    ( ( modproc (stolfi-grab-module-and-proc "[^.a-zA-Z0-9_]") )
      mcomps fname proc defpat found-module
    )
    ; (message (concat "py-vmap: modproc = " modproc))
    (if modproc
      (progn
        (setq mcomps (split-string modproc "[.]") )
        ; (message (concat "py-vmap: mcomps = " (prin1-to-string mcomps)))
        (setq proc (car (last mcomps)))
        ; (message (concat "py-vmap: proc = " (prin1-to-string proc)))
        (setq mcomps (butlast mcomps))
        ; (message (concat "py-vmap: mcomps = " (prin1-to-string mcomps)))
        (setq defpat (concat "^[ ]*def[ ]+" proc "\\b"))
        ; (message (concat "py-vmap: defpat = " (prin1-to-string defpat)))
        (setq fname (concat (string-join mcomps "/") ".py"))
        ; (message (concat "py-vmap: fname = " (prin1-to-string fname)))
        (setq found-module (stolfi-visit-module-and-proc arg fname defpat))
        ; (message (concat "py-vmap: found-module = " (prin1-to-string found-module)))
      )
      (error "no valid function call here")
    )
  )
)