# Buggy code
def _groupby_and_aggregate(self, grouper, how, *args, **kwargs):
    """revaluate the obj with a groupby aggregation"""

    if grouper is None:
        self._set_binner()
        grouper = self.grouper

    obj = self._selected_obj

    try:
        grouped = groupby(obj, by=None, grouper=grouper, axis=self.axis)
    except TypeError:
        # panel grouper
        grouped = PanelGroupBy(obj, grouper=grouper, axis=self.axis)

    try:
        result = grouped.aggregate(how, *args, **kwargs)
    except Exception:
        # we have a non-reducing function
        # try to evaluate
        result = grouped.apply(how, *args, **kwargs)

    result = self._apply_loffset(result)

    return self._wrap_result(result)


# Traceback (TypeError)
In [38]: pd.Series(1, index=pd.period_range(start='2000', periods=100)).resample('M').count()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-38-295afa97781f> in <module>()
----> 1 pd.Series(1, index=pd.period_range(start='2000', periods=100)).resample('M').count()

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in f(self, _method)
473
474     def f(self, _method=method):
--> 475         return self._groupby_and_aggregate(None, _method)
476     f.__doc__ = getattr(GroupBy, method).__doc__
477     setattr(Resampler, method, f)

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _groupby_and_aggregate(self, grouper, how, *args, **kwargs)
353
354         if grouper is None:
--> 355             self._set_binner()
356             grouper = self.grouper
357

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _set_binner(self)
202
203         if self.binner is None:
--> 204             self.binner, self.grouper = self._get_binner()
205
206     def _get_binner(self):

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _get_binner(self)
210         """
211
--> 212         binner, bins, binlabels = self._get_binner_for_time()
213         bin_grouper = BinGrouper(bins, binlabels)
214         return binner, bin_grouper

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _get_binner_for_time(self)
538         if self.kind == 'period':
539             return self.groupby._get_time_period_bins(self.ax)
--> 540         return self.groupby._get_time_bins(self.ax)
541
542     def _downsample(self, how, **kwargs):

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _get_time_bins(self, ax)
905         if not isinstance(ax, DatetimeIndex):
906             raise TypeError('axis must be a DatetimeIndex, but got '
--> 907                             'an instance of %r' % type(ax).__name__)
908
909         if len(ax) == 0:

TypeError: axis must be a DatetimeIndex, but got an instance of 'PeriodIndex'

# Fixed code
def _groupby_and_aggregate(self, grouper, how, *args, **kwargs):
    if grouper is None:
        return self._downsample(how, **kwargs)
    return super(PeriodIndexResampler, self)._groupby_and_aggregate(
        grouper, how, *args, **kwargs
    )