Looping

Backwards

> for i in reversed(range(5)):
    print(i)
...
4
3
2
1
0

List Backwards

> my_list = ['a', 'b', 'c', 'd', 'e']
> for i in reversed(range(0, len(my_list))):
    print(my_list[i])
...
e
d
c
b
a

Basic Loop

> my_list = ['a', 'b', 'c', 'd', 'e']
> for x in range(len(my_list)):
    print(x)
...
0
1
2
3
4

Enumerate

> my_list = ['a', 'b', 'c', 'd', 'e']
> for count, value in enumerate(my_list):
>   print(count, value)
...
0 a
1 b
2 c
3 d
4 e

Front / Back Same Time

> my_list = ['a', 'b', 'c', 'd', 'e']
> for i in range(len(my_list) // 2):
>   print(my_list[i], my_list[~i])
...
a e
b d
# NOTE: It does not reach the middle element for an odd length

While/For Else

counter = 0
while counter <= 5:
  print counter,
  counter += 1
else:
  print "loop exited normally"
# Output: 0 1 2 3 4 5 loop exited normally

for i in range(5):
  print i,
  if i > 3:
   break
else:
  print "loop exited normally"
# Output: 0 1 2 3 4

Continue

Continues the next iteration of the loop

> for num in range(2, 10):
...     if num % 2 == 0:
...         print("Found an even number", num)
...         continue
...     print("Found an odd number", num)
...

Pass

It does nothing, can be used when a statement requires an action

> while True:
...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)

Break

The break statement, like in C, breaks out of the innermost enclosing for or while loop.

> for n in range(2, 10):
...     for x in range(2, n):
...         if n % x == 0:
...             print(n, 'equals', x, '*', n//x)
...             break
...     else:
...         # loop fell through without finding a factor
...         print(n, 'is a prime number')