Note that list and array are different classes. You can do:
del mylist[:]
This will actually modify your existing list. David’s answer creates a new list and assigns it to the same variable. Which you want depends on the situation (e.g. does any other variable have a reference to the same list?).
Try:
a = [1,2]
b = a
a = []
and
a = [1,2]
b = a
del a[:]
Print a and b each time to see the difference.