Iterate through python string starting at index

Question

If I have a very long string (say 100 million characters), is there a way to iterate through the characters using something like for c in str: but starting a certain number of characters in? I'd prefer not to slice the string and use a subset, because I understand that slicing the string will make a copy (very expensive in my case). In other words, can I specify a start point for an iterator over a string?

Answer 1

In python3 range is an generator, and not a list. That means that the following code will not require excessive memory:

for i in range(start_pos, len(my_string)):
   print(my_string[i])

If you'd rather use an iterator over my_string then you need to write it yourself:

def iter_starting_at(start_pos, string):
    for i in range(start_pos, len(string)):
        yield string[i]

for character in iter_starting_at(start_pos, my_string):
    print(character)

Answer 2

you can do it using string indexes, like it's list:

for i in xrange(100, 200):
    print(s[i])