code: def col_isdt(df,col_name = None):
      
      col_list = df.select_dtypes(include = 'datetime').columns
      if col_name is None:
          return col_list
      else:
          return col_name in col_list
docs: Returns a list of columns that are of type 'datetime'. If col_name is specified, returns 
      whether the column in the DataFrame is of type 'datetime' 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 'datetime'