os.path.expanduser does not seem to expand $HOME on Mac (only variations on ~), but os.path.expandvar does successfully expand $HOME (and any other variables in the path)
Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
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>>> import os
>>> os.environ['HOME']
'/Users/david'
>>> os.path.expanduser('$HOME')
'$HOME'
>>> os.path.expanduser('$HOME/')
'$HOME/'
>>> os.path.expanduser('~')
'/Users/david'
>>> os.path.expanduser('~david')
'/Users/david'
>>> os.path.expandvars('$HOME')
'/Users/david'
os.path.expanduser does not seem to expand $HOME on Mac (only variations on ~), but os.path.expandvar does successfully expand $HOME (and any other variables in the path)