This is going to be a short one.
For many tasks, we iterate using for loops of this sort:
#Example: Getting odd numbers out of a list
some_list = [x for x in range(5,20)]
#Boring
for i in range(len(some_list)):
value = some_list[i]
if value%2 != 0:
print value
# Neat!
for i,value in enumerate(some_list):
if value%2 != 0:
print value
Basically, enumerate() returns an iterator with the tuple of (index,item)
Bonus tip: if for some reason you don't like to count from zero, you can add an offset using enumerate(list,offset).
As an example, I haven't seen aisles numbered 0 anywhere, so:
grocery_store =['apples','mangoes','oranges', 'guavas']
for i, fruit in enumerate(grocery_store,1):
print "We have {} at Aisle #{}".format(fruit,i)
To which you have the following sensible output:
We have apples at Aisle #1
We have mangoes at Aisle #2
We have oranges at Aisle #3
We have guavas at Aisle #4
Start using it already!