If you only want one item's count, use the count method:
>>> [1, 2, 3, 4, 1, 4, 1].count(1)
Don't use this if you want to count multiple items. Calling count in a loop requires a separate pass over the list for every count call, which can be catastrophic for performance. If you want to count all items or even just multiple items, use Counter, as explained in the other answers.