scores = {'alice': 92, 'bob': 85, 'carol': 78}

scores['dave'] = 88        # add a new pair
scores['bob'] = 90         # update an existing value
del scores['carol']        # remove a pair

print(scores)               # {'alice': 92, 'bob': 90, 'dave': 88}
print(len(scores))          # 3
print('alice' in scores)    # True (checks keys, not values)