Python: building a reduce function with lambda

I need to define a function, that reduces a list to a single integer. The function takes two arguments. A "combiner": telling us how the list should be reduced and the list itself. The following is the demanded result:

Combines elements in the list lst using a combiner function.
    As you can see, the combiner function takes two arguments.
    It reduces the list to a single integer, depending on the combiner function.

>>> reduce(lambda x, y: x + y, [1, 2, 3, 4])
10
>>> reduce(lambda x, y: x * y, [1, 2, 3, 4])
24
>>> reduce(lambda x, y: x * y, [4])
4

I struggle with the point on how to correctly define the first argument. How can I program which function should be used on the list? Or do I even need to make an If/Else-Statement here?

My intuition till now:

def reduce(combiner, lst):
  plus_func = lambda x, y: x + y
  mult_func = lambda x, y: x * y
  if combiner == plus_func:
    n = 0
    for i in lst:
      n += i
    return n
  elif combiner == x * y:
    n = 1
    for i in lst:
      n * i
    return n

How can I tell the function which lambda to apply?

>Solution :

You need to use the function (lambda) that is passed to the reduce:

def reduce(combiner, lst):
    res = lst[0]
    for v in lst[1:]:
        res = combiner(res, i)
    return n