Dictionary Data Type In Python

What is Dictionary Data Type?

Dictionary is a built in data type which allows us key-value pair. It is also referred as associative array or hash table. The dictionary is unordered and mutable data structure which helps us to store and access data associated with their keys. The key of dictionary should be unique and immutable. Your key may be string, number or tuple. Values can be of any type. The dictionary data items are enclosed within pair of curly brackets and key and value are separated with colon (:). The dictionary are used to map to data sets such as roll number and name of students or keyword and its definition, person name and their phone number.

How to Create Dictionary:
1.      

my_dict={'fruit1':'apple','fruit2':'banana'}

print(my_dict)

Output:

{'fruit1': 'apple', 'fruit2': 'banana'}

In the above example my_dict is dictionary name and fruit1, fruit2 are the keys with its values apple and banana respectively. In this example both key and values are string type.

2.      

my_dict={1:'apple',2:'banana'}

print(my_dict)

Output:

{1: 'apple', 2: 'banana'}

In this example dictionary is created with keys 1,2 are the numeric type and values are string type.

3.      

my_dict={'apple':1,'banana':2}

my_dict

Output:

{'apple': 1, 'banana': 2}

 

In this example dictionary is created with key string type and values are numeric type. Here apple and banana are keys and 1,2 are values.

4.     Dictionary with dict keyword:

my_dict=dict(apple=1,banana=2,carrot=3,flower=4)

print(my_dict)

{'apple': 1, 'banana': 2, 'carrot': 3, 'flower': 4}

In this example we have created dictionary with dict keyword. Here curly bracket is not used to enclose the dictionary. Because the dict() it is builtin function and function come with pair of parenthesis. In dict() parenthesis the key value pair is stored.

How to Access Dictionary Elements:?      

my_dict={'apple':1,'banana':2}

print(my_dict['apple'])

Output:

1

We can access the values of dictionary by using key.  In above example apple is key and we have accessed its value 1 by accessing key apple.

Another Example,

my_dict={'fruit1':'apple','fruit2':'banana'}

print(my_dict['fruit1'])

Output:

Apple

Here we have accessed apple value through the key fruit1.  In the above example only one value is accessed by using key name in square bracket. But if we want to access all values from the dictionary then we can use loop.

For Loop to Access all values from Dictionary:

my_dict1={"fruit1":"Apple","Fruit2":"Banana"}

for key in my_dict1:

    print(my_dict1[key])

Output:

Apple

Banana

Here all keys are accessed with for loop and in this way we can access values of keys. He key is loop variable which is used to access keys.

Another example,

dict1={1:10,2:20,3:30,4:40,5:50,6:60}

for key in dict1:

    print(key,dict1[key])

Output:

1 10

2 20

3 30

4 40

5 50

6 60

Here we have accessed all keys and in square bracket again given key so compiler will access all values associated with keys.

List of Methods/ Functions used for Dictionary:

1.     Len() Function:

The len() method return the number of key values pair from dictionary.

For example,

dict1={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

print(len(dict1))

Output:

4

In above dictionary total 4 key-value pairs stored in dictionary. So len() function returned 4 as an output.

2.     Keys() Method:

The keys() method returns list of all the keys present in your dictionary.

For example,

dict1={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

print(dict1.keys())

Output:

dict_keys([1, 2, 3, 'Fruits'])

3.     The values() Method:

The values() function returns list of all the values in your dictionary.

For example,

dict1={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

print(dict1.values())

Output:

dict_values(['banana', 'Apple', 'Grapes', 'Pineapple'])

4.     The items() Method:

This function returns list of all key-value pairs.

For example,

dict1={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

print(dict1.items())

Output:

dict_items([(1, 'banana'), (2, 'Apple'), (3, 'Grapes'), ('Fruits', 'Pineapple')])

5.     The get() Method:

The get() method is used to get a specified key’s value.

For example,

dict1={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

print(dict1.get(1))

print(dict1.get("fruits"))

Output:

banana

None

In this example in first print function with the get method passed value 1 i.e. 1 is a key present in dictionary dict1. And its associated value is banana. So compiler has displayed banana as an output.

In second print function with get() passed the key fruits. But fruits key not present, Fruit key is present so compiler has displayed None.

6.     The pop():

The pop() function removes a specified key-value pair from dictionary. For example,

dict1={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

print(dict1.pop(2))

print(dict1)

Output:

Apple

{1: 'banana', 3: 'Grapes', 'Fruits': 'Pineapple'}

In above example pop function is applied on dict1 dictionary. In pop() function 2 is passed. This is the key in your dictionary and its associated value is Apple.   When you display your dictionary after applying pop function then it will not display Apple value.

7.     The update():

This function helps to update the key value pair from dictionary.

dict1={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

dict1.update({2:"Apple1"})

print(dict1)

Output:

{1: 'banana', 2: 'Apple1', 3: 'Grapes', 'Fruits': 'Pineapple'}

In the parenthesis of update function, the second key 2 has updated with Apple1. Its old value is Apple.

8.     The clear():

The clear() function helps to clear your dictionary. It helps to remove all key values pairs from dictionary.

For example,

dict2={1:"banana",2:"Apple",3:"Grapes","Fruits":"Pineapple"}

dict2.clear()

print(dict2)

Output:

{}

The compiler will return empty dictionary.

 

For Loop on keys():

dict1={1:10,2:20,3:30,4:40,5:50,6:60,7:13,8:"Hello"}

for key in dict1.keys():

    print(key)

1

2

3

4

5

6

7

8

The keys() helps to access all keys.

For Loop on items():

dict1={1:10,2:20,3:30,4:40,5:50,6:60,7:13,8:"Hello"}

for key,value in dict1.items():

    print(key,value)

Output:

1 10

2 20

3 30

4 40

5 50

6 60

7 13

8 Hello

 

For Loop on values():

dict1={1:10,2:20,3:30,4:40,5:50,6:60,7:13,8:"Hello"}

for key in dict1.values():

    print(key)

10

20

30

40

50

60

13

Hello

 

Python program to print the sum of all values in Dictionary

dict1={1:10,2:20,3:30,4:40,5:50,6:60,7:13,8:"Hello"}

sum=0

for i in dict1.values():

    if isinstance(i,int):

        sum=sum+i

print("The sum of all values in dictionary is:",sum)

 

Output:

The sum of all values in dictionary is: 223

 

In above code isinstance() function is used to include only integer values from dictionary. In our dictionary the 8^th key have string value but on string value the addition is not possible. So isinstance() method is applied on dictionary in in parenthesis the loop variable I and int keyword is passed. So now when compiler will execute the code by taking only the numeric values.

 

User Input for Dictionary:

my_dict = {} #Empty dictionary

n = int(input("Enter the number of key-value pairs: "))

for i in range(n):

    key = input("Enter the key: ")

    value = input("Enter the value: ")

    my_dict[key] = value

print("My dictionary is:", my_dict)

Output:

Enter the number of key-value pairs: 3

Enter the key: DBMS

Enter the value: 50

Enter the key: C++

Enter the value: 67

Enter the key: Python

Enter the value: 90

My dictionary is: {'DBMS': '50', 'C++': '67', 'Python': '90'}

The for loop is used to take user input for dictionary. The number of key value pair will be accepted by compiler as per the user input you have stored in n. In above example user input for key value pair is 3 so total 3 key value pairs will be accepted by compiler.