Ankit Kumar

Posted on May 10, 2023 • Edited on Jun 1, 2023

Dictionary in Python

#python #algorithms #beginners #programming

Dictionary is a data structure in python which store as a key:value pair.
Dictionaries do not allow duplicate keys, since it uses hashing concep store keys.

Overview of most used Dictionary Methods

1. declaring a dictionary

dictionary = {}

2. Inserting Key:Value pairs

we have a specific syntax to do it, as shown below.
example:-

 dictionary['name'] = 'ankit'
 print(dictionary) 
 # output  :  { 'name' : 'ankit' }

3. Accessing a Value using Key

There are two ways you can access a value using key
In python, there is a method .get() which takes a key as a argument, used to get a value as shown
.get() will return None , if key is not found in a dictionary
The other way to access a value is using square brackets,

        value = dictionary.get('name')
        print(value)
        #output: 'milk'
        value = dictionary.get('unknown_key')
        print(value)
        #output : None
        # other way
        name = dictionary['name']
        print(name)
        #output: 'milk'

4. Methods used while looping a Dictionary

items() :

The items() method in Python dictionaries returns a view object that contains the key-value pairs of the dictionary as tuples.
example:-

my_dict = {'apple': 2, 'banana': 3, 'cherry': 5}
for key, value in my_dict.items():
    print(key, value)
#output apple 2
        banana 3
        cherry 5

5 .keys():

This method will return dict_keys which are list of keys in a dictionary. we can use loops to access all the keys. example:-

        keys = my_dict.keys()
        for key in keys:
            print(key)
        #output: apple
                 banana
                 cherry

6 .values():

This method will return dict_values which are list of values in a dictionary. we can use loops to access all the values.
example:-
```
    values = my_dict.values()
    for value in values:
        print(value)
    #output: 2 3 5
    ```
```

7. in:

It is a keyword which can be used to find weather the key is present or not it will return a boolean value as shown example:-

        boolean = 'banana' in my_dict
        print(boolean)
        #output: True
        boolean = 'unknown_key' in my_dict
        print(boolean)
        #output: False

8. update():

This will take another dictionary as argument and addes it to the old one
example:-

    new_dict = { 'Lemon' : 10 }
    my_dict.update(new_dict)
    print(my_dict)
    #output: {'apple': 2, 'banana': 4, 'cherry': 5, 'Lemon':10}

9 .copy():

This method copies the entire dictionary to the new one example:-

         new_dict = my_dict.copy()
         print(new_dict)
        #output: {'apple': 2, 'banana': 4, 'cherry': 5,   'Lemon':10}

10. Update existing key using Square Brackets

We can append a key value pair in to a dictionary or we can update a value using the key as shown. example:-

     my_dict = {'apple': 2, 'banana': 3, 'cherry': 5}
my_dict['banana'] = 4
print(my_dict)
#output : {'apple': 2, 'banana': 4, 'cherry': 5}

11 .pop('key'):

This method will take key as a argument and will remove the key value pair from dictionary as shown
It will return a value of the key that was poped
This will through KeyError if key is not found example:-

my_dict = {'apple': 2, 'banana': 3, 'cherry': 5}
my_dict.pop('banana')
print(my_dict)
#output {'apple': 2, 'cherry': 5}

12. popitem():

This method will pop the last item that was inserted and will return a tuple of key and value
This will return KeyError if dictionary is empty example:-

my_dict = {'apple': 2, 'banana': 3, 'cherry': 5}
item = my_dict.popitem()
print(item)
print(my_dict)
#output ('cherry', 5)
      {'apple': 2, 'banana': 3}

13 .clear():

This method will clear the dictionary and returns None example:-

        my_dict.clear() 
        print(my_dict)
        #output: {}

14 .setdefault()

Returns the value of a key if the key is in the dictionary else inserts the key with a value to the dictionary example:-

my_dict = {'apple': 2, 'banana': 3, 'cherry': 5}
value = my_dict.setdefault('banana', 10)
print(value)
print(my_dict)

value = my_dict.setdefault('orange', 7)
print(value)
print(my_dict)
#0utput 3
             {'apple': 2, 'banana': 3, 'cherry': 5}
            7
           {'apple': 2, 'banana': 3, 'cherry': 5, 'orange': 7}

DEV Community