Python3.6 map() function

1. The use of the map() function in Python 3.6 is different from that in 2.7. When calculating the length len(), you will get the following error

D=map(set,dataSet)

numItems = float ( len (D))

Using the map() function in Python 3.6 is different from that in 2.7. When calculating the length len(), you will get the following error:

TypeError: object of type 'map' has no len()

Solution: To get the same effect, add a list()

D=list(map(set,dataSet))

numItems = float ( len (D))