Traceback (most recent call last):
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/tseries/frequencies.py", line 624, in get_offset
    klass = prefix_mapping[split[0]]
KeyError: 'Y'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/tseries/frequencies.py", line 550, in to_offset
    offset = get_offset(name)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/tseries/frequencies.py", line 630, in get_offset
    raise ValueError(_INVALID_FREQ_ERROR.format(name))
ValueError: Invalid frequency: Y

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/core/handlers/exception.py", line 41, in inner
    response = get_response(request)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/core/handlers/base.py", line 187, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3.6/contextlib.py", line 52, in inner
    return func(*args, **kwds)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/views/generic/base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/contrib/auth/mixins.py", line 56, in dispatch
    return super(LoginRequiredMixin, self).dispatch(request, *args, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/utils/decorators.py", line 67, in _wrapper
    return bound_func(*args, **kwargs)
  File "/usr/lib/python3.6/contextlib.py", line 52, in inner
    return func(*args, **kwds)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/viewflow/decorators.py", line 213, in _wrapper
    return view(request, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/utils/decorators.py", line 63, in bound_func
    return func.__get__(self, type(self))(*args2, **kwargs2)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/viewflow/flow/views/task.py", line 70, in dispatch
    return super(BaseFlowMixin, self).dispatch(request, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/views/generic/base.py", line 88, in dispatch
    return handler(request, *args, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/django/views/generic/edit.py", line 174, in get
    return self.render_to_response(self.get_context_data())
  File "/home/henrytebs/projects/property-mode/erisk/e_risk/banks/mixins.py", line 283, in get_context_data
    annual_change_df = self.get_annual_change_df(df, geo_data)
  File "/home/henrytebs/projects/property-mode/erisk/e_risk/banks/mixins.py", line 264, in get_annual_change_df
    sect_mkt_df = get_market_activity_df(sect_sales_15, 'year', 'sale_amount', 'approval_date')
  File "/home/henrytebs/projects/property-mode/erisk/e_risk/valuations/market_activity.py", line 39, in get_market_activity_df
    .dt.to_period(periods_freqs[period])
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/core/base.py", line 211, in f
    return self._delegate_method(name, *args, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/core/indexes/accessors.py", line 133, in _delegate_method
    result = method(*args, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/core/indexes/datetimes.py", line 944, in to_period
    return PeriodIndex(self.values, name=self.name, freq=freq, tz=self.tz)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/core/indexes/period.py", line 229, in __new__
    freq = Period._maybe_convert_freq(freq)
  File "pandas/_libs/period.pyx", line 700, in pandas._libs.period._Period._maybe_convert_freq (pandas/_libs/period.c:11195)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/util/_decorators.py", line 91, in wrapper
    return func(*args, **kwargs)
  File "/home/henrytebs/.virtualenvs/erisk/lib/python3.6/site-packages/pandas/tseries/frequencies.py", line 557, in to_offset
    raise ValueError(_INVALID_FREQ_ERROR.format(freq))
ValueError: Invalid frequency: Y