Join Lists with + Operator :

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
list3 = list1 + list2                   # Concatenate two lists
print(list3)

Output :

['a', 'b', 'c', 1, 2, 3]

Join Lists Using Loop and append() :

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]

for x in list2:                         # Loop through second list
    list1.append(x)                     # Append items to first list

print(list1)

Output :

['a', 'b', 'c', 1, 2, 3]

Join Lists Using extend() :

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]

list1.extend(list2)                    # Extend first list with second
print(list1)

Output :

['a', 'b', 'c', 1, 2, 3]