Why not use len(alist) in an iterator?

[Pedroski55]

Python lists are integer-indexed arrays. That is why you can retrieve an element from the list with a number: alphabet[13]

I often read you shouldn't use len(alist) like this (Although, I also see this often.):

for i in range(len(alphabet)):
    # do something

I would like to know why this is said.

The only reason I can think of is: enumerate is a generator, which is small.

However, unless the lists we are using are ginormous, you will not notice the difference on a modern computer. People who are tempted to create giant lists will, in all probability, put the list values in some form of database and use a generator to access the database instead, thereby not using giant lists at all.

from string import ascii_lowercase

alphabet = [a for a in ascii_lowercase]
for a in alphabet:
    print(a, end=' ')

for i in range(len(alphabet)):
    print(alphabet[i], end=' ')

for num, value in enumerate(alphabet, start=5):
    print(f'num = {num}, value =  {value}', end=' ')

gen = enumerate(alphabet, 5)
next(gen) # (5, 'a') enumerate is a generator

I don't know how enumerate works, but I can easily fake it:

# fake enumerate function
def my_enum(alist, num):
    for v in alist:
        tup = (alist.index(v) + num, v)
        yield tup

gen = my_enum(alphabet, 5)
next(gen) # (5, 'a')

If a list is not very big in memory, why should I complicate matters with enumerate to reach exactly the same end?

The generator seems more complicated and less straightforward.

gen = ((ascii_lowercase.index(a), a) for a in ascii_lowercase)
start = 5
for index, value in gen:
    print(f'index = {index + start}, value = {value}')