[python] Python: Total sum of a list of numbers with the for loop

I'm new to Python and I have this problem:

I need to program a Python function that gives me back the sum of a list of numbers using a for loop.

I just know the following:

sum = 0
for x in [1,2,3,4,5]:
      sum = sum + x

print(sum)

x=[1,2,3,4,5]
sum=0
for s in range(0,len(x)):
   sum=sum+x[s]
print sum   

l = [1,2,3,4,5]
sum = 0
for x in l:
    sum = sum + x

And you can change l for any list you want.