Python Dictionaries

What are Python Dictionaries :

Dictionaries are Python’s implementation of a data structure that could also be known as an array. A dictionary consists of a collection of key-value pairs. Each key-value pair maps the key to its associated value.

Syntax :

Dictionaries are declared by using curly braces and a colon … like this

{ key : value }

The colon shows the separation between the key and the value. The Keys and Values stored in the dictionary can be a string, list, tuple, another dictionary, a float, or a number.

Accessing elements in a dictionary :

Let’s take the following as our example of a dictionary

my_dict={1 : “hello”, 2 : “bye”}

To access “hello” you have to specify the key which it is stored in. The current key is 1 so you would do something like this…

print(my_dict[1])

This line of code is accessing key 1 if you run this code your output will be…

“hello”

In this example I specified 1 so I will get an output of “hello” if you specify 2 then your output will be “bye”

Changing elements in a dictionary :

We will use the same dictionary as our example.

my_dict={1 : “hello”, 2 : “bye”}

To change hello to hi, you can one again specify the key and then change the value.

(my_dict [1] ) = “hi”

This will change what is stored in the dictionary but it will not give you an output. To see what is changed you have to print the dictionary.

print(my_dict)

Your output will be…

{1 : “hi”, 2 : “bye”}

Adding Elements into a Dictionary :

If the key is already present, then the existing value gets updated. In case the key is not present, a new key: value pair is added to the dictionary.

my_dict={1 : “hello”, 2 : “bye”}

To add another key:value pair you can do the following…

my_dict [3] = “see you”print(my_dict)

The output will be…

my_dict={1 : “hello”, 2 : “bye”, 3 : “see you”}

Removing Elements from a Dictionary :

1. We can remove a particular item in a dictionary by using the pop() method
2. All the items can be removed at once, using the clear() method
3. We can also use the del keyword to remove individual items or the entire dictionary itself

1: pop()

This method removes an item with the provided key and returns the value

This is the dictionary example…

squares = {1:1, 2:4, 3:9, 4:16, 5:25}

To “pop out” the number 16, access key 4

print(squares.pop(4))

The output will be 16 but if you print the squares it will look something like this…

{1:1, 2:4, 3:9, 5:25}

2:clear()

Let’s say you want to remove the whole squares dictionary. You could use clear to do that.

squares.clear()print(squares)

The output will be…

{ }

You are getting an empty dictionary because everything is cleared out.

3:del[]

Ok, let’s bring back the squares variable and redefine it.

squares = {1:1, 2:4, 3:9, 4:16, 5:25}

To delete the third key you can use the del function. The del function does not print the key that is deleted but instead just deletes it.

del squares[3]

This line of code will delete key 3, when you print the dictionary your end result will be the following…

{1: 1, 2: 4, 4: 16, 5: 25}

Python Dictionary Methods :

1: get()

The get() method returns the value of the item with the specified key.

dictionary.get(keyname, value)

Parameter Values

This is going to be our dictionary example

tech={"brand": "apple", "model": "iphone 12", "year": 2021}

Using the get function

x = apple.get(“price”, 15000)
print(x)

This output will be…

15000

Let’s see what will happen if you print tech

print(tech)

The output is…

{"brand": "apple", "model": "iphone 12", "year": 2021}

Nothing changed. The get function is not permanent you can use it and get an output, but when you print the tech variable it will stay the same.

2: items()

The items() method returns a view object. The view object contains the key-value pairs of the dictionary, as tuples in a list.

dictionary.items()

We will use the same dictionary

tech={"brand": "apple", "model": "iphone 12", "year": 2021}

Let’s make a variable to store the items method in

x=tech.items()
print(x)

This output will show you everything that is stored in the dictionary in groups

dict_items([('brand', 'apple'), ('model', 'iphone 12'), ('year', 2021)])

3: keys()

The keys() method returns a view object. The view object contains the keys of the dictionary, as a list.

dictionary.keys()

Once again, we are going to use the same dictionary

tech={"brand": "apple", "model": "iphone 12", "year": 2021}
x=tech.keys()

This will print all the keys in tech

dict_keys(['brand', 'model', 'year'])