code: def convert_types_slow(df):
      '''This is a slow operation.'''
      dtypes = get_types(df)
      for k, v in dtypes.items():
          t = df[df['key']==k]
          t['value'] = t['value'].astype(v)
      df = df.apply(convert_row, axis=1)
      return df convert_types_slow(df):
      '''This is a slow operation.'''
      dtypes = get_types(df)
      for k, v in dtypes.items():
          t = df[df['key']==k]
          t['value'] = t['value'].astype(v)
      df = df.apply(convert_row, axis=1)
      return df
docs: This is a slow operation.