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