5.10: “Equal To One Of” Trick with the in Operator

The expression event.key in (K_LEFT, K_a) is just a Python trick to make the code simpler. It is a way of saying "evaluate to True if event.key is equal to one of K_LEFT or K_a". The following two expressions will evaluate the exact same way:

event.key in (K_LEFT, K_a)
event.key == K_LEFT or event.key == K_a

You can really save on some space by using this trick when you have to check if a value is equal to one of multiple values. The following two expressions will evaluate the exact same way:

spam == 'dog' or spam == 'cat' or spam == 'mouse' or spam == 'horse' or spam == 42 or spam == 'dingo'
spam in ('dog', 'cat', 'mouse', 'horse', 42, 'dingo')

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