Cannot index an array - causing key error , context astropy.io

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There seems to be a problem indexing the object class 'astropy.io.fits.hdu.hdulist.HDUList

When I try to index it, I get a key Error as if it were a dictionary:

fits_image_filename = "/tmp/chiCyGQHY.fits"
from astropy.io import fits
hdul = fits.open(fits_image_filename)

print(type(hdul))
len(hdul)
<class 'astropy.io.fits.hdu.hdulist.HDUList'>
1

I need to extract hdul[0]. I succeed ONLY if I do hdul.pop()

hdu=hdul.pop()

hdu

<astropy.io.fits.hdu.image.PrimaryHDU object at 0x7f707f89c510>

However if instead I do hdu = hdul[0]
**KeyError**                                  Traceback (most recent call last)
<ipython-input-25-e993ae5dfe6a> in <module>()
----> 1 hdul**[Integer(0)]**

/home/patricia/SageMath/local/lib/python2.7/site-packages/astropy/io/fits/hdu/hdulist.pyc in __getitem__(self, key)
    299         try:
    300             return self._try_while_unread_hdus(super(HDUList, self).__getitem__,
--> 301                                             self._positive_index_of(key))
    302         except IndexError as e:
    303             # Raise a more helpful IndexError if the file was not fully read.

/home/patricia/SageMath/local/lib/python2.7/site-packages/astropy/io/fits/hdu/hdulist.pyc in _positive_index_of(self, key)
    719         """
    720 
--> 721         index = self.index_of(key)
    722 
    723         if index >= 0:

/home/patricia/SageMath/local/lib/python2.7/site-packages/astropy/io/fits/hdu/hdulist.pyc in index_of(self, key)
    684                 '{} indices must be integers, extension names as strings, '
    685                 'or (extname, version) tuples; got {}'
--> 686                 ''.format(self.__class__.__name__, _key))
    687 
    688         _key = (_key.strip()).upper()

KeyError: 'HDUList indices must be integers, extension names as strings, or (extname, version) tuples; got 0'

Question: What causes this confusion in sage between dictionaries and lists. Is it the wrapper Integer() ? If so, what is a more elegant work-around ?

Thanks to all you mavens out there!

Pat