Cambrigde exam python task - assistance needed

I'm preparing for an exam that's coming up soon about python and seem to have gotten stuck with a task.

The task says as follows:

Data is received as a stream of characters:

• each stream of characters is a sequence of surnames
• the start and end of a sequence is indicated by two * characters (**)
• the surnames are separated by a # character

A typical character sequence is:

**ali#thomas#ghandi#akmar#smith#barija**

Write program code to:

• input a character sequence (made up of one or more surnames

• check that the character sequence has a valid format

• calculate and output the number of surnames*

If anybody out there would be kind enough to help me out, even if it's just a little bit, I would be very grateful.

Thank you all very much for your time.

Cheers, Ben