Using enumerate() for operations between the elements of a list

Question

Until now, given a list L, i was using range(len(L)) to access its elements:

L = [4, 3, 5, 2, 7]

for i in range(len(L)):
    print(i, "-", L[i])

However, I've read that this approach is not pythonic and there's a function called enumerate that can do the work as well:

L = [4, 3, 5, 2, 7]

for i, n in enumerate(L):
    print(i, "-", n)

Now, allow me to propose a problem to show the trouble I've been experiencing with this approach:

Given a list of integers L, transform the list so that every element n in the resulting list is the sum of the elements up to n in the initial list.

Using the first approach that would be:

L = [4, 3, 5, 2, 7]

for i in range(1, len(L)):
    L[i] = L[i] + L[i - 1]

When trying the second approach:

L = [4, 3, 5, 2, 1]

for i, n in enumerate(L): #It starts at element 0!
    L[i] = n + L[i - 1]

The questions that result from this problem are the following:

• How can I make enumerate start at element 1?
• Is the second approach actually worth it in this case?
• If the previous answer is "no", when is it worth it?

Answer 1

Answering to How can I make enumerate start at element 1

You do that this way:

L = [4, 3, 5, 2, 1] for i, n in enumerate(L, start=1):

Answer 2

Here's some solutions to this particular problem:

L = [4, 3, 5, 2, 7]

# Solution 0
print([sum(L[0:i + 1]) for i in range(len(L))])

# Solution 1
res = [0]
for i, n in enumerate(L):
    res.append(res[-1] + n)

print(res[1:])

# Solution 2
for i, n in enumerate(L[1:]):
    L[i + 1] = L[i + 1] + L[i]
print(L)