sys._getframe() not behaving as expected

[Skip Montanaro]

sys._getframe() is acting peculiar.  At least it doesn't seem to be doing
what I expect based upon a couple readings of its doc.  Given this module
(call it 'gl'):

    import sys

    def printframes():
        print "frame[-2]:", id(sys._getframe(-2))
        print "frame[-1]:", id(sys._getframe(-1))
        print "frame[0]:", id(sys._getframe(0))
        print "frame[-2] globals:", id(sys._getframe(-2).f_globals)
        print "frame[-1] globals:", id(sys._getframe(-1).f_globals)
        print "frame[0] globals:", id(sys._getframe(0).f_globals)
        print "my globals:", id(globals())

calling it like so from the interpreter prompt (CVS):

    >>> import gl
    >>> def f():
    ...   gl.printframes()
    ... 
    >>> f()
    frame[-2]: 3822448
    frame[-1]: 3822448
    frame[0]: 3822448
    frame[-2] globals: 11889232
    frame[-1] globals: 11889232
    frame[0] globals: 11889232
    my globals: 11889232
    >>> id(globals())
    3955136

The gl.printframes() function never prints the id of the interpreter's
globals(), nor does it ever print different frames.  What am I missing?  I
would like to get a handle on the globals for the frame from which
printframes() is called.

Skip