Dictionaries|Dictionaries And Identity Operators DictionariesAndIdentityOperators

Dictionaries

Dictionaries can have keys of any immutable type, like integers or tuples even list, not just strings.

elements = {"hydrogen": 1, "helium": 2, "carbon": 6}# attention mutable can't be used as a key in dictionary print(elements["helium"])# print the value mapped to "helium" elements["lithium"] = 3# insert "lithium" with a value of 3 into the dictionary animals = {'dogs': [20, 10, 15, 8, 32, 15], 'cats'(this is the key): [3,4,2,8,2,4](this is the value), 'rabbits': [2, 3, 3], 'fish': [0.3, 0.5, 0.8, 0.3, 1]} # the example of defining the lists as values # The result of animals['dogs'][3] is 8

attention mutable can't be used as a key in dictionary

Look Up

print("carbon" in elements) print(elements.get("dilithium")) # output: True None

Identity Operators

You can check if a key returned None with the is operator. You can check for the opposite using is not.

n = elements.get("dilithium") print(n is None) print(n is not None)

Compound Data Structures In Dictionary Defined

elements = {"hydrogen": {"number": 1, "weight": 1.00794, "symbol": "H"}, "helium": {"number": 2, "weight": 4.002602, "symbol": "He"}}

Access Elements

helium = elements["helium"]# get the helium dictionary hydrogen_weight = elements["hydrogen"]["weight"]# get hydrogen's weight

Add

oxygen = {"number":8,"weight":15.999,"symbol":"O"}# create a new oxygen dictionary elements["oxygen"] = oxygen# assign 'oxygen' as a key to the elements dictionary print('elements = ', elements) # output: elements ={"hydrogen": {"number": 1, "weight": 1.00794, "symbol": 'H'}, "helium": {"number": 2, "weight": 4.002602, "symbol": "He"}, "oxygen": {"number": 8, "weight": 15.999, "symbol": "O"}}