comp_classes = {150 : 'Programming 1',
                151 : 'Programming 2',
                170 : 'Introduction To Software Development',
                245 : 'Data Structures'}
                
print(comp_classes[150])
del comp_classes[170]
comp_classes[170] = 'Intro to Soft Dev'
print (len(comp_classes))
print(comp_classes.get(245))
print(comp_classes.keys()) #returns a list
print(comp_classes.values()) #returns a list