docs: def col_isobj(df, col_name = None):
      """ Returns a list of columns that are of type object. If col_name is specified, returns 
      whether the column in the DataFrame is of type 'object' instead.
      Parameters:
      df - DataFrame
          DataFrame to check
      col_name - string, default None
          If specified, this function will True if df[col_name] is of type 'object'
      """
      col_list = df.select_dtypes(include = 'object').columns
      if col_name is None:
          return col_list
      else:
          return col_name in col_list