Flow of Control

if, elif and else choose what runs; for with range() and while repeat it; break and continue change a loop; nested loops print patterns.

Key ideas

In an if–elif–else chain only the first true branch runs; else runs when no condition is true.
range(a, b, c) starts at a, goes in steps of c and stops before b; range(n) gives 0 to n − 1.
A while loop repeats while its condition is True, so something in its body must change for it to stop.
break leaves the loop at once; continue skips the rest of this pass and starts the next one.
In nested loops the inner loop runs right through on every pass of the outer loop.
Indentation (usually 4 spaces) shows which lines belong to an if, an else or a loop.
Number programs use % 10 for the last digit and // 10 to drop it; Fibonacci uses a, b = b, a + b.

range()	list(range(5)) = [0, 1, 2, 3, 4]; list(range(1, 10, 3)) = [1, 4, 7]
Adding 1 to n	sum of range(1, n + 1) = n(n + 1)/2: 1 to 10 gives 55
Nested loops	range(3) inside range(4): the inner body runs 12 times
Special numbers	Armstrong: 153 = 1³ + 5³ + 3³; perfect: 28 = 1 + 2 + 4 + 7 + 14
break	for i in range(1, 30): if i * i > 50: break print(i) # 8
continue	for i in range(1, 8): if i % 3 == 0: continue print(i, end=' ') # 1 2 4 5 7

What are a, b and c after these lines run?
a, b, c = 72, 52, 86
if a > b:
    a, b = b, a
if b > c:
    b, c = c, b
if a > b:
    a, b = b, a

Working: each swap puts the smaller value first: the three numbers end up sorted

Answer: a = 52, b = 72, c = 86