Slicing

seq[start:stop:step] — any of the three can be omitted.

Rules

• start defaults to 0, stop to len(seq), step to 1
• Negative indices count from the end (-1 is the last)
• The slice never raises on out-of-range — it just clamps

Slicing returns a copy, not a view

b = a[:] is the idiomatic shallow copy of a list.

Try it

1. Take every third character of "abcdefghij".
2. Get the middle third of a 30-element list.