code: def add(self, other, axis="columns", level=None, fill_value=None):
          
          return self._binary_op(
              "add", other, axis=axis, level=level, fill_value=fill_value
          )
docs: Add this DataFrame to another or a scalar/list.
  
          Args:
              other: What to add this this DataFrame.
              axis: The axis to apply addition over. Only applicaable to Series
                  or list 'other'.
              level: A level in the multilevel axis to add over.
              fill_value: The value to fill NaN.
  
          Returns:
              A new DataFrame with the applied addition.