Using tuples as keys in dictionaries
Since tuples are hashable, and list is not, we must use tuple as the key if we need to create a composite key to use in a dictionary.
Example: We would come across a composite key if we need to create a telephone directory that maps, first-name, last-name, pairs of telephone numbers, etc. Assuming that we have declared the variables as last and first number, we could write a dictionary assignment statement as shown below:
directory[last,first] = number
Inside the brackets, the expression is a tuple. We could use tuple assignment in a for loop to navigate this dictionary.
for last, first in directory:
print first, last, directory[last, first]
This loop navigates the keys in the directory, which are tuples. It assigns the elements of each tuple to last and first and then prints the name and corresponding telephone number.
Tuples and dictionaryDictionary can return the list of tuples by calling items, where each tuple is a key value pair.
a = {'x':100, 'y':200}
b = list(a.items())
print(b)
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