Python has a syntax for ternary since 2.5.
The syntax for this is
if condition if not b, where the condition is a boolean.
You can rewrite your code as follows:
discounted_price = original_ticket_price - discount_value discounted_price if discounted_price> = 0 otherwise 0
Personally, I have trouble reading, but it's another way to write your code.
EDIT you can find more info about ternary in this article