title: Statsmodel using ARMA
body: <p>A bit new here but trying to get a statsmodel ARMA prediction tool to work.  I've imported some stock data from Yahoo and gotten the ARMA to give me fitting parameters.  However when I use the predict code all I receive is a list of errors that I don't seem to be able to figure out.  Not quite sure what I'm doing wrong here:</p>
  
  <pre><code>import pandas
  import statsmodels.tsa.api as tsa
  from pandas.io.data import DataReader
  
  start = pandas.datetime(2013,1,1)
  end = pandas.datetime.today()
  
  data = DataReader('GOOG','yahoo')
  arma =tsa.ARMA(data['Close'], order =(2,2))
  results= arma.fit()
  results.predict(start=start,end=end)
  </code></pre>
  
  <p>The errors are:</p>
  
  <pre><code>---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  C:\Windows\system32\&lt;ipython-input-84-25a9b6bc631d&gt; in &lt;module&gt;()
       13 results= arma.fit()
       14 results.summary()
  ---&gt; 15 results.predict(start=start,end=end)
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\base\wrapp
  er.pyc in wrapper(self, *args, **kwargs)
       88         results = object.__getattribute__(self, '_results')
       89         data = results.model.data
  ---&gt; 90         return data.wrap_output(func(results, *args, **kwargs), how)
       91
       92     argspec = inspect.getargspec(func)
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\tsa\arima_
  model.pyc in predict(self, start, end, exog, dynamic)
     1265
     1266         """
  -&gt; 1267         return self.model.predict(self.params, start, end, exog, dynamic
  )
     1268
     1269     def forecast(self, steps=1, exog=None, alpha=.05):
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\tsa\arima_
  model.pyc in predict(self, params, start, end, exog, dynamic)
      497
      498         # will return an index of a date
  
  --&gt; 499         start = self._get_predict_start(start, dynamic)
      500         end, out_of_sample = self._get_predict_end(end, dynamic)
      501         if out_of_sample and (exog is None and self.k_exog &gt; 0):
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\tsa\arima_
  model.pyc in _get_predict_start(self, start, dynamic)
      404             #elif 'mle' not in method or dynamic: # should be on a date
  
      405             start = _validate(start, k_ar, k_diff, self.data.dates,
  --&gt; 406                               method)
      407             start = super(ARMA, self)._get_predict_start(start)
      408         _check_arima_start(start, k_ar, k_diff, method, dynamic)
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\tsa\arima_
  model.pyc in _validate(start, k_ar, k_diff, dates, method)
      160     if isinstance(start, (basestring, datetime)):
      161         start_date = start
  --&gt; 162         start = _index_date(start, dates)
      163         start -= k_diff
      164     if 'mle' not in method and start &lt; k_ar - k_diff:
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\tsa\base\d
  atetools.pyc in _index_date(date, dates)
       37         freq = _infer_freq(dates)
       38         # we can start prediction at the end of endog
  
  ---&gt; 39         if _idx_from_dates(dates[-1], date, freq) == 1:
       40             return len(dates)
       41
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\tsa\base\d
  atetools.pyc in _idx_from_dates(d1, d2, freq)
       70         from pandas import DatetimeIndex
       71         return len(DatetimeIndex(start=d1, end=d2,
  ---&gt; 72                                  freq = _freq_to_pandas[freq])) - 1
       73     except ImportError, err:
       74         from pandas import DateRange
  
  D:\Python27\lib\site-packages\statsmodels-0.5.0-py2.7.egg\statsmodels\tsa\base\d
  atetools.pyc in __getitem__(self, key)
       11         # being lazy, don't want to replace dictionary below
  
       12         def __getitem__(self, key):
  ---&gt; 13             return get_offset(key)
       14     _freq_to_pandas = _freq_to_pandas_class()
       15 except ImportError, err:
  
  D:\Python27\lib\site-packages\pandas\tseries\frequencies.pyc in get_offset(name)
  
      484     """
      485     if name not in _dont_uppercase:
  --&gt; 486         name = name.upper()
      487
      488         if name in _rule_aliases:
  
  AttributeError: 'NoneType' object has no attribute 'upper'
  </code></pre>