code: def add(self, col: str, value):
          
          try:
              self.df[col] = value
          except Exception as e:
              self.err(e, self.add, "Can not add column")
docs: Add a column with default values
  
          :param col: column name
          :type col: str
          :param value: column value
          :type value: any
  
          :example: ``ds.add("Col 4", 0)``