Dictionary in Python

 Dictionary

         Dictionary in Python is an unordered collection of data values, used to store data values like a dictionary which unlike other data types that hold only single value as an element. Dictionary holds Key: Value pair. Each Key-Value pair in a dictionary is separated by colon ( : ), whereas each key is separated by 'comma'.The dictionary is defined into element Keys and values.

• Keys must be a single element

• Value can be any type such as list, tuple, integer, etc.

Creating Dictionary

       In Python a dictionary can be created by placing a sequence of elements within curly braces {}, separated by 'comma'. Values in a dictionary can be of any data type and can be duplicated, whereas keys can not be repeated and must be immutable.

         

           Dictionary can also be created by the built-in function dict(). An empty dictionary can be created by just placing to curly braces {}.

Syntax

1. Dict = {"Name": "technicalgupta", "Age": 22}    

 Example

# creating empty dictionary

dict={}

print(dict)

# creating a dictionary with integer keys

dict={1:'btech',2:'second',3:'year'}

print(dict)

# creating a dictionary with mixed keys

dict={'name':'technicalgupta',1:[1,2,3,4]}

print(dict)

# with dict() method

dict=dict({1:'btech',2:'second',3:'year'})

print(dict)

Output

{ }

{1:'btech',2:'second',3:'year'}

{'name':'technicalgupta',1:[1,2,3,4]}

{1:'btech',2:'second',3:'year'}

Note : Dictionary keys are case sensitive, same name but different cases of key will be treated distinctly.

Accessing the dictionary elements

              In order to access the items of a dictionary refer to its key name. Key can be used inside square brackets. There is also a method called get() that will also help in accessing the element of a dictionary.

Example

# creating a dictionary 

Dict={1:'technicalguptaji','name':'sunny',3:'gupta'}

#accessing element using key

print(Dict['name'])

#accessing element using get() method

print(Dict.get(3))

Output

sunny

gupta

Adding elements into a dictionary

            One value at a time can be added to a dictionary by defining value along with the key. like Dict[key]='value'. Updating an existing values in a dictionary can be done by using the built-in update() method.

Note : While adding a value ,if the key value already exists, the value gets updated otherwise a new key with the value is added to the dictionary.

Example 

1. # Creating an empty Dictionary   
2. Dict = {}   
3. print("Empty Dictionary: ")   
4. print(Dict)   
5.     
6. # Adding elements to dictionary one at a time   
7. Dict[0] = 'technical'  
8. Dict[2] = 'gupta'  
9. Dict[3] = 'ji'  
10. print("Dictionary after adding 3 elements: ")   
11. print(Dict)   
12.     
13. # Updating existing Key's Value   
14. Dict[3] = 'class'  
15. print("Updated key value: ")   
16. print(Dict)    

Output

Empty Dictionary:
{}

Dictionary after adding 3 elements:
{0: 'technical', 2: 'gupta', 3: 'ji'}

Updated key value:
{0: 'Peter', 2: 'Joseph', 3: 'class'}

Removing elements from Dictionary

       In Python dictionary deletion of keys can be done by using the del keyword. using del keyword, specific values from a dictionary as well as whole dictionary can be deleted. Other function like pop() and popitem() can also be used for deleting specific values and arbitrary values from a dictionary. All the items from the dictionary can be deleted at once by using clear() method.

Example

# Initial dictionary

Dict={5:'welcome',6:'to',7:'technical',8:'guptaji'}

print(Dict)

# Deleting a key value

del Dict[6]

print(Dict)

# Deleting a key using pop() method

Dict.pop(5)

print(Dict)

# Deleting entire dictionary

Dict.clear()

print(Dict)

Output

{5:'welcome',6:'to',7:'technical',8:'guptaji'}

{5:'welcome',7:'technical',8:'guptaji'}

{7:'technical',8:'guptaji'}

{}