In [1]: from astropy.time import Time

In [2]: t = Time([], format='iso')
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-e9a03eac829b> in <module>()
----> 1 t = Time([], format='iso')

~/Dropbox/Code/Astropy/astropy/astropy/time/core.py in __init__(self, val, val2, format, scale, precision, in_subfmt, out_subfmt, location, copy)
    348         else:
    349             self._init_from_vals(val, val2, format, scale, copy,
--> 350                                  precision, in_subfmt, out_subfmt)
    351             self.SCALES = TIME_TYPES[self.scale]
    352 

~/Dropbox/Code/Astropy/astropy/astropy/time/core.py in _init_from_vals(self, val, val2, format, scale, copy, precision, in_subfmt, out_subfmt)
    403         # Parse / convert input values into internal jd1, jd2 based on format
    404         self._time = self._get_time_fmt(val, val2, format, scale,
--> 405                                         precision, in_subfmt, out_subfmt)
    406         self._format = self._time.name
    407 

~/Dropbox/Code/Astropy/astropy/astropy/time/core.py in _get_time_fmt(self, val, val2, format, scale, precision, in_subfmt, out_subfmt)
    454                 pass
    455         else:
--> 456             raise ValueError('Input values did not match {0}'.format(err_msg))
    457 
    458     @classmethod

ValueError: Input values did not match the format class iso

In [9]: t[1:1]
Out[9]: ---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
~/miniconda3/envs/dev/lib/python3.7/site-packages/IPython/core/formatters.py in __call__(self, obj)
    700                 type_pprinters=self.type_printers,
    701                 deferred_pprinters=self.deferred_printers)
--> 702             printer.pretty(obj)
    703             printer.flush()
    704             return stream.getvalue()

~/miniconda3/envs/dev/lib/python3.7/site-packages/IPython/lib/pretty.py in pretty(self, obj)
    398                         if cls is not object \
    399                                 and callable(cls.__dict__.get('__repr__')):
--> 400                             return _repr_pprint(obj, self, cycle)
    401 
    402             return _default_pprint(obj, self, cycle)

~/miniconda3/envs/dev/lib/python3.7/site-packages/IPython/lib/pretty.py in _repr_pprint(obj, p, cycle)
    693     """A pprint that just redirects to the normal repr function."""
    694     # Find newlines and replace them with p.break_()
--> 695     output = repr(obj)
    696     for idx,output_line in enumerate(output.splitlines()):
    697         if idx:

~/Dropbox/Code/Astropy/astropy/astropy/time/core.py in __repr__(self)
    580         return ("<{0} object: scale='{1}' format='{2}' value={3}>"
    581                 .format(self.__class__.__name__, self.scale, self.format,
--> 582                         getattr(self, self.format)))
    583 
    584     def __str__(self):

~/Dropbox/Code/Astropy/astropy/astropy/time/core.py in __getattr__(self, attr)
   1409                 else:
   1410                     tm = self.replicate(format=attr)
-> 1411                 value = tm._shaped_like_input(tm._time.to_value(parent=tm))
   1412                 cache[attr] = value
   1413             return cache[attr]

~/Dropbox/Code/Astropy/astropy/astropy/time/formats.py in to_value(self, timezone, parent)
    667         iterator = np.nditer([iys, ims, ids, ihrs, imins, isecs, ifracs, None],
    668                              flags=['refs_ok'],
--> 669                              op_dtypes=7*[iys.dtype] + [object])
    670 
    671         for iy, im, id, ihr, imin, isec, ifracsec, out in iterator:

ValueError: Iteration of zero-sized operands is not enabled