key = lambda x : code example

Example: lambda x:x[1]

student_tuples = [
    ('john', 'A', 15),
    ('jane', 'B', 12),
    ('dave', 'B', 10),]
sorted(student_tuples, key=lambda student: student[2])   # sort by age
>>>>[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]