How is del D and del D[<key>] different from one another if D is a dictionary ?

Create a dictionary named D with three entries, for keys 'a', 'b' and 'c'. What happens if you try to index a nonexistent key (D['d']) ? What does python do if you try to assign to a nonexistent key d.
(e.g., D['d'] = 'spam') ?

Discuss Bubble sort and Insertion sort techniques.

What will be the output produced by following code fragments?

y = str(123)
x = "hello" * 3
print (x, y)
x = "hello" + "world"
y = len(x)
print (y, x)