Updating the obsolete Pandas package pd.ewma () to pd.Dataframe.ewm ()

I had a code that averaged exponentially from the pandas pd.ewma ()

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-67-d81f5301d1c0> in <module>
     55 
     56     # Smoothing the plot
---> 57     predictions_df_list['ewma'] = pd.ewma(predictions_df_list["prices"], span=20, freq="D") #pd.DataFrame.ewma
     58     predictions_df_list['actual_value'] = test['prices']
     59     predictions_df_list['actual_value_ewma'] = pd.ewma(predictions_df_list["actual_value"], span=20, freq="D")

AttributeError: module 'pandas' has no attribute 'ewma'

I found out that the package was in disuse. I tried to change to pd.Dataframe.ewm() but

---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
<ipython-input-68-681b235459d9> in <module>
     55 
     56     # Smoothing the plot
---> 57     predictions_df_list['ewma'] = pd.DataFrame.ewm(predictions_df_list["prices"], span=20) #pd.DataFrame.ewma
     58     predictions_df_list['actual_value'] = test['prices']
     59     predictions_df_list['actual_value_ewma'] = pd.DataFrame.ewm(predictions_df_list["actual_value"], span=20)

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\frame.py in __setitem__(self, key, value)
   3117         else:
   3118             # set column
-> 3119             self._set_item(key, value)
   3120 
   3121     def _setitem_slice(self, key, value):

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\frame.py in _set_item(self, key, value)
   3192 
   3193         self._ensure_valid_index(value)
-> 3194         value = self._sanitize_column(key, value)
   3195         NDFrame._set_item(self, key, value)
   3196 

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\frame.py in _sanitize_column(self, key, value, broadcast)
   3385             value = _sanitize_index(value, self.index, copy=False)
   3386 
-> 3387         elif isinstance(value, Index) or is_sequence(value):
   3388             from pandas.core.series import _sanitize_index
   3389 

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\dtypes\inference.py in is_sequence(obj)
    470 
    471     try:
--> 472         iter(obj)  # Can iterate over it.
    473         len(obj)   # Has a length associated with it.
    474         return not isinstance(obj, string_and_binary_types)

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\window.py in __iter__(self)
    184     def __iter__(self):
    185         url = 'https://github.com/pandas-dev/pandas/issues/11704'
--> 186         raise NotImplementedError('See issue #11704 {url}'.format(url=url))
    187 
    188     def _get_index(self, index=None):

NotImplementedError: See issue #11704 https://github.com/pandas-dev/pandas/issues/11704

And it seems on the GitHub page that the current implementation does not use an explicit iterator, but rather an sliding window in python and marginal calculations.

So, how can I update this method?