python list concatenation efficiency

Question

What is the most efficient way to concatenate two lists list_a and list_b when:

• list_b items have to be placed before

Answer 1

You can assign list_b to a slice, which happens to be empty but at the start of list_a:

list_a[0:0] = list_b

This is the fastest way to insert a list into another list, at any position.