11.7. Using Tuples as Keys in Dictionaries¶
Because tuples are hashable and lists are not, if we want to create a composite key to use in a dictionary we must use a tuple as the key.
We would encounter a composite key if we wanted to create a telephone
directory that maps from last-name, first-name pairs to telephone
numbers. Assuming that we have defined the variables
number, we could write a dictionary
assignment statement as follows:
directory[last, first] = number
Write code to create a dictionary called ‘d1’, and in it give the tuple (1, ‘a’) a value of “tuple”.
The expression in brackets is a tuple. We could use tuple assignment in
for loop to traverse this dictionary.
for last, first in directory: print(first, last, directory[last, first])
This loop traverses the keys in
directory, which are
tuples. It assigns the elements of each tuple to
first, then prints the name and corresponding telephone