[Tutor] os.environ weirdness

[Poor Yorick]

Another phenomenon I haven't made sense of:

 >>> for i in os.environ:
    print i

   
Traceback (most recent call last):
  File "<pyshell#13>", line 1, in ?
    for i in os.environ:
  File "C:\Python22\lib\os.py", line 387, in __getitem__
    return self.data[key.upper()]
AttributeError: 'int' object has no attribute 'upper'

I realize that os.environ is not a builtin dictionary, but some sort of 
subclassed dictionary, but these commands work:

os.environ.keys()
os.environ.items()

doesn't the "in" statement just resolve to one of those functions?

Regards,

Poor Yorick
gp@pooryorick.com