intersection in python 3.9 code example

Example 1: insert python3

a = [1,2,3,4,5]

#a.insert(index_to_insert_at, num_to_insert)
a.insert(0, -1)

# a is now: [-1,1,2,3,4,5]

Example 2: python list comprehension

#example: removing common elements found in `a` from `b`.
a = [1,2,3,4,5]
b = [5,6,7,8,9]
# desired output: [1,2,3,4]

# gets each item found in `a` AND not in `b`
print([i for i in a if i not in b])