I have a pandas frame. When I print the columns (shown below), its turns out that my columns are out of order. Is there a way to sort only the first 30 columns so they are in order (30,60,90...900)? 

```
[in]   df.columns

[out]  Index(['120', '150', '180', '210', '240', '270', '30', '300', '330', '360',
   '390', '420', '450', '480', '510', '540', '570', '60', '600', '630',
   '660', '690', '720', '750', '780', '810', '840', '870', '90', '900',
   'Item', 'Price', 'Size', 'Time', 'Type', 'Unnamed: 0'],
  dtype='object')

```

The fixed frame would be as follows:

```
[out]  Index(['30','60','90,'120', '150', '180', '210', '240', '270','300', '330', '360',
   '390', '420', '450', '480', '510', '540', '570','600', '630',
   '660', '690', '720', '750', '780', '810', '840', '870','900',
   'Item', 'Price', 'Size', 'Time', 'Type', 'Unnamed: 0'],
  dtype='object')

```