I'm looking at the code for the combinations on the python documentation for itertools (https://docs.python.org/2/library/itertools.html)

```
def combinations(iterable, r):
# combinations('ABCD', 2) --> AB AC AD BC BD CD
# combinations(range(4), 3) --> 012 013 023 123
pool = tuple(iterable)
n = len(pool)
if r > n:
return
indices = range(r)
yield tuple(pool[i] for i in indices)
while True:
for i in reversed(range(r)):
if indices[i] != i + n - r:
break
else:
return
indices[i] += 1
for j in range(i+1, r):
indices[j] = indices[j-1] + 1
yield tuple(pool[i] for i in indices)
```

On the line where it says indices[i] += 1, why is it able to find 'i' ? As far as I understand once you are out of the for loop (which starts right after while True), variable 'i' should not exist (just like the i mentioned in the first yield sentence) !!!

Also can someone explain the logic in english ? I understand until the first yield but then I'm lost. Thanks in advance.