Use break and continue to do this. Breaking nested loops can be done in Python using the following:

for a in range(...):
   for b in range(..):
      if some condition:
         # break the inner loop
         break
   else:
      # will be called if the previous loop did not end with a `break` 
      continue
   # but here we end up right after breaking the inner loop, so we can
   # simply break the outer loop as well
   break

Another way is to wrap everything in a function and use return to escape from the loop.

You're returning immediately in both the if and else blocks. That ends the loop in both cases.

You should only return in the if block. If you make it through the entire loop without returning, you know that all the words are title case.

def all_title_case(word_list): 
    for word in word_list: 
        if not word.istitle():
            return False
    return True 

You can also use the all() function instead of a loop.

def all_title_case(word_list): 
    return all(word.istitle() for word in word_list)

for filename in filenames[:100]:
    outline= getinfo(filename)
    outfile.write(outline)

The list slice filenames[:100] will truncate the list of file names to just the first 100 elements.

The best equivalent in Python would be a while-loop:

i = 0
while i < A.length: # If `A` is a regular Python container type, use `len()`
    do_things(A[i])
    if  is_true(i):
        i -= 1
    i += 1

Note however, as said in the comments, iterating like this over a container is more often than not, a bad idea. You should review your code and make sure you actually need this behavior.

EDIT

It's just a sloppy explanation of a loop that doesnt continue to the next element until some condition is met. I didn't explain clear enough I guess

Use continue instead then. Decrementing i is the wrong action:

i = 0
while i < A.length:
    do_things(A[i])
    if not is_true(i):
        continue
    i += 1

Better yet, you can ditch the while-loop all together and use enumerate:

for i, el in enumerate(A):
    if not is_true(el):
        continue
    # do work