When to use range function in python for loops

Question

If we are able to create a for loop without using the range function, as in:

foods = [potato, pizza, spinach]

for food in foods:
  print(food)

why am I not able to do the same in this following nested for loops?

def exponents(bases, powers):
  results = []

  for i in range(len(bases)):
    for j in range(len(powers)):
      results.append(bases[i]**powers[j])
  return results

rather using this approach:

def exponents(bases, powers):
  results = []

  for i in bases:
    for j in powers:
      results.append(bases[i]**powers[j])
  return results

will result in an indexError:

IndexError: list index out of range

What is the difference between the single and nested for loops in regards to these variables?

Answer 1

When you use the range function, you are iterating the list index. When you use the list directly, you are iterating the objects in the list.

Try this:

def exponents(bases, powers):
  results = []

  for b in bases:
    for p in powers:
      results.append(b**p)
  return results  # not new