Equivalent for pop on strings

you can convert the string to a list. list(string) and pop it, or you could iterate in chunks slicing the list [] or you can slice the string as is and iterate in chunks

You can wrap the string in a StringIO or BytesIO and pretend it's a file. That should be pretty fast.

from cStringIO import StringIO
# or, in Py3/Py2.6+:
#from io import BytesIO, StringIO

s = StringIO(large_string)
while True:
    chunk = s.read(200)
    if len(chunk) > 0:
        process(chunk)
    if len(chunk) < 200:
        break