Flatten a list/tuple and Call a function with tuples

[beginner]

Hi,

I am wondering how do I 'flatten' a list or a tuple? For example, I'd
like to transform[1, 2, (3,4)] or [1,2,[3,4]] to  [1,2,3,4].

Another question is how do I pass a tuple or list of all the
aurgements of a function to the function. For example, I have all the
arguments of a function in a tuple a=(1,2,3). Then I want to pass each
item in the tuple to a function f so that I make a function call
f(1,2,3). In perl it is a given, but in python, I haven't figured out
a way to do it. (Maybe apply? but it is deprecated?)

Thanks,
cg