Applications

Using Dictionaries in our code

To initialize a new dictionary you would use curly braces:

dictionary = {}

Once you have created your dictionary, you can start adding key value pairs to it. The key must be a string,float,integer or tuple. The value can be any type of data structure you would like including a list or set

Below is a couple of examples of adding different types of keys and values to the dictionary.

1. Adding a integer key and string value
   • Lets imagine an example where we would like to map each letter to its placement in the alphabet. In this example, I will show how to map the first few letters.

            

                
                    # create the dictionary
d = {}

# add to it
d['a'] = 1
d['b'] = 2
d['c'] = 3
d['d'] = 4

#print it out
print(d)
                
            
        

This prints out: {'a': 1, 'b': 2, 'c': 3, 'd': 4}

• One thing to take into account is that it may look ordered but really, it has no absolute order.

1. Keys

To access all the keys in a dictionary, you will use the method .keys()

            

                
                    # Declare the dictionary
d= {'a': 1, 'b': 2, 'c': 3, 'd': 4}

# print out the keys
print(d.keys())
                
            
        

This prints out dict_keys(['a', 'b', 'c', 'd']) which can be iterated through in a for loop.

3. Values

To access all the values that the key pairs point to, you will use the method .values

            

                
                    # Declare the dictionary
d= {'a': 1, 'b': 2, 'c': 3, 'd': 4}

# print out the values
print(d.values())
                
            
        

This returns dict_values([1, 2, 3, 4]) which can be iterated through.

4. Items

To access all the items in a dictionary, you will use the method .items()

            

                
                    # Declare the dictionary
d= {'a': 1, 'b': 2, 'c': 3, 'd': 4}

# print the items
print(d.items())
                
            
        

This returns a list of tuples that contain each item in the dictionary. Once again you can iterate through this list of tuples.

5. Looking up values by a Key

This is where a dictionary comes in super useful. You can look up the value associated with any of the keys.

            

                
                    # Declare the dictionary
d= {'a': 1, 'b': 2, 'c': 3, 'd': 4}

# Print out the value that corresponds to a
print(d['a'])
                
            
        

This would print the value 1 since the keya` has a value of 1 associated with it. This can be done with any key in a dictionary, but will return an error if you try to use a key that does not exist in a dictionary.

You can check to see if a dictionary contains a specific key by using the in operator.

            

                
                    d= {'a': 1, 'b': 2, 'c': 3, 'd': 4}
'a' in d #True
'f' in d #False
                
            
        

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