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Python Dictionary




Python – Dictionary


As we read earlier about Python Tuples , Now we will study about Dictionary in python. In the python programming language, this is our third collection of data type. In this, we will cover python dict, create a dictionary python , how to use dictionary in python, python key value, python dict example etc. so let’s start reading about the second collection data type. 





Dictionary in python

Dictionary is a collection or sequence of key – values pair type of elements. Dictionary is mutable datatype i.e. they can be edited or modified.

In python programming dictionaries are written with Curly Brackets.



Python dict syntax :

dictionary variable = { comma separated element }

Note : Element is a pair of key and values. where,

key = Any immutable datatype
value = Any datatype



Python dict example :

          key  value   key  value     key  value      key  value
           ↓    ↓       ↓    ↓         ↓     ↓         ↓     ↓
dict_1 = {'a' : 1,     'b' : 22,      'c' : 333,      'd' : 4444}
print(dict_1)



Output :

{'a': 1, 'b': 22, 'c': 333, 'd': 4444}




How to access the items from a dictionary ?

We can access the dictionary items by using its key name.



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
print(dict_1['c'])



Output :

333




CRUD for dictionary

CRUD Operation are those basic and important operation which one should know how to apply after studying “Dictionary” data type.



C – CREATE

Our first operation of CRUD which is “C” for create which means either to add elements or to insert them.



How to add items in a dictionary ?

We can add items into dictionary by using the new index key and assigning a value in it.



Syntax for add items :

dict_1[key] = value



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
dict_1['e'] = 55555
print(dict_1)



Output :

{'a': 1, 'b': 22, 'c': 333, 'd': 4444, 'e': 55555}




R – READ

Our second operation of CRUD which is ” R ” for read which means either to read data or to search data from the dictionary.



How to access items from a dictionary ?

This is an alternative method to access the dictionary items by using the get( ) function.



Syntax for access items :

variable = dict_1.get( key )



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
x = dict_1.get("c")
print(x)



Output :

333




U – UPDATE

Our third operation of CRUD which is “U” for update operation is used to modify the contents of a list or to make changes in a dictionary.



How to change / update the values ?

We can change / update the value of a specific item by using its key name.



General syntax for update values :

dictionary_variable[key] = value



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
dict_1['b']=22222
print(dict_1)

Output :

{'a': 1, 'b': 22222, 'c': 333, 'd': 4444}




There is an alternative to update the dictionary values.



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
dict_2 = {'e':55555}
dict_1.update(dict_2)
print(dict_1)



Output :

{'a': 1, 'b': 22, 'c': 333, 'd': 4444, 'e': 55555}




D – DELETE

Our last operation of CRUD which is “D” for delete operation is used to remove an element from the dictionary.



How to remove the items ?

We can remove the items by using the pop( ) function with the specified key name.



General syntax for removing items :

dictionary_variable.pop( key )



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
dict_1.pop('c')
print(dict_1)



Output :

{'a': 1, 'b': 22, 'd': 4444}




Python Loop through dictionary

In dictionary datatype, we can use only element loop. There are some element loops which is used in dictionary are:




We can print all the key names one by one which is given in the dictionary. 



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
for e in dict_1:
print(e)



Output :

a
b
c
d

The above loop always return keys of the dictionary.




We can print all the key names one by one which is given in the dictionary with the different loop.



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
for e in dict_1.keys():
print(e)



Output :

a
b
c
d

This loop always return keys of the dictionary.




We can print all the values one by one which is given in the dictionary.



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
for e in dict_1.values():
print(e)



Output :

1
22
333
4444

This loop always return values of the dictionary.




We can print both keys and values which is given in the dictionary.



Example :

dict_1 = {'a':1, 'b':22, 'c':333, 'd':4444}
for e in dict_1.items():
print(e)



Output :

('a', 1)
('b', 22)
('c', 333)
('d', 4444)

This loop always return tuple datatype.





Nested dictionary Python

Nested dictionary means putting a dictionary inside another dictionary is called Nested dictionary. In other words, python dictionary inside dictionary.



Example :

dict_1 = {'A': {'a':1}, 'B':{'b':22}}
print(dict_1)



Output :

{'A': {'a': 1}, 'B': {'b': 22}}




Python dict( ) constructor

This is an alternative method to create a dictionary by using dict( ) constructor.



Example :

dict_1 = dict(a = 1, b = 2, c = 3)
print(dict_1)



Output :

{'a': 1, 'b': 2, 'c': 3}




Dictionary Python Functions

1. len( ) : To check how many items a dictionary has, by using the len( ) function.

2. clear( ) : It removes all the elements from the given dictionary.

3. copy( ) : Returns a copy of the dictionary.

4. del( )The del keyword removes the item with the specified key name and also del python dictionary completely.


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