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Python Dictionary is used to store multiple items in key:value pair in a single variable . Python Dictionary is surrounded by curly braces ({}) . Python provides total 4 built-in data types to store collection of data of which one is Dictionary . The other data types are List , Set and Tuple .
How to create a Dictionary in Python ?
There are multiple ways to create a Python Dictionary –
- Using curly braces (
{}) - using
dict()function - Using dictionary comprehension
To check if it is a dictionary or not we can use type() function .
# Creating a dictionary in Python
# Using curly braces ({})
dictionary_from_bracket = {"Rajkumar":1,"apple":2,True:3,1:4,2.5:5,10:6}
print(dictionary_from_bracket)
# checking the type
print("type of dictionary_from_bracket",type(dictionary_from_bracket))
# using dict() function
dictionary_from_function = dict((("Rajkumar",1),("apple",2),(True,3),(1,4),(2.5,5),(10,6)))
print(dictionary_from_function)
# checking the type
print("type of dictionary_from_function",type(dictionary_from_function))
# using dictionary comprehension
dictionary_from_comprehension = {item:(item+5) for item in range(5)}
print(dictionary_from_comprehension)
# checking the type
print("type of dictionary_from_comprehension",type(dictionary_from_comprehension)){'Rajkumar': 1, 'apple': 2, True: 4, 2.5: 5, 10: 6}
type of dictionary_from_bracket <class 'dict'>
{'Rajkumar': 1, 'apple': 2, True: 4, 2.5: 5, 10: 6}
type of dictionary_from_function <class 'dict'>
{0: 5, 1: 6, 2: 7, 3: 8, 4: 9}
type of dictionary_from_comprehension <class 'dict'>
- In the above code we have created dictionary using various ways
- First we have created dictionary using curly braces (
{}) . Then we have printed the dictionary and also its type . - Second we have created dictionary using
dict(). Then we have printed the dictionary and also its type . - Third we have created dictionary using dictionary comprehension . Then we have printed the dictionary and also its type .
- From the output we can see that in every case type is dictionary .
Note :
Dictionary items are separated by comma (,) and it can be of any type as we have seen in the previous code .
Characteristics of a Dictionary in Python
Python dictionary is unindexed , ordered and mutable(changeable) collection of items . Dictionary key can not be duplicate but we can use duplicate values as dictionary value .
Python Dictionary is unindexed | How to access value in dictionary Python
Python Dictionary is unindexed it means we can not access dictionary items using its index . If we try to do that it will raise KeyError .
Example 1:
mydictionary = {"Rajkumar":1,"apple":2,True:3,"Apple":4,2.5:5,None:6}
print(mydictionary[2])---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
C:\Users\RAJKUM~1\AppData\Local\Temp/ipykernel_8092/535005601.py in <module>
1 mydictionary = {"Rajkumar":1,"apple":2,True:3,"Apple":4,2.5:5,None:6}
----> 2 print(mydictionary[2])
KeyError: 2
In the above code when we have tried to access dictionary items using its index it has raised an error . Actually when we have written mydictionary[2] program has checked whether 2 is in dictionary key or not . As 2 is not a dictionary key so the program raised an KeyError .
So if we give valid dictionary key between the square bracket then the program should not give any error . Now we will see how to access value in dictionary Python using dictionary key with examples –
Example 2:
# Declaring a dictionary
mydictionary = {"Rajkumar":1, "apple":2,True:3,"Apple":4,2.5:5,None:6}
# accessing value of Rajkumar key
print(mydictionary["Rajkumar"])
# accessing value of True key
print(mydictionary[True])1 3
- In the above code first we have declared a dictionary named
mydictionaryas{"Rajkumar":1, "apple":2, True:3, "Apple":4, 2.5:5, None:6}which have 6 key"Rajkumar","apple",True,"Apple",2.5,Nonewhose corresponding values are1,2,3,4,5,6. - After that we have printed value of
"Rajkumar"key which printed1in the output . - Then we have printed value of
Truekey which printed3in the output .
Python Dictionary is ordered
Dictionary items are ordered it means that it maintains a defined order and we can not change it .
Note :
Before Python version 3.7 Dictionary items were unordered .
Python Dictionary is mutable | How to update a Dictionary in Python ?
Python dictionary is mutable it means we can change , delete and add items in the dictionary .
Example 1:
# Declaring a dictionary
mydictionary = {"Rajkumar":1,"apple":2,True:3,"Apple":4,2.5:5,None:6}
# printing the dictionary
print(mydictionary)
# updating the dictionary using its key
mydictionary["Rajkumar"]=11
# printing the updated dictionary
print(mydictionary){'Rajkumar': 1, 'apple': 2, True: 3, 'Apple': 4, 2.5: 5, None: 6}
{'Rajkumar': 11, 'apple': 2, True: 3, 'Apple': 4, 2.5: 5, None: 6}
- In the above code first we have declared a dictionary then we have printed the dictionary .
- Then we have changed the value of
"Rajkumar"key with11. - After that we have printed the new dictionary .
Python Dictionary does not allow duplicate key
Previously we have seen that we can access any value of a dictionary using its key . So if a Python dictionary has more than one key with same name , when we want to access value using key, Python will not understand value of which key we want to access . For this reason key in Python dictionary can not be duplicate .
How to delete a Dictionary in Python ?
We can delete a dictionary in Python using del keyword . But if we want to access the dictionary after deleting it using del keyword it will raise a NameError .
Example:
# Declaring a dictionary
mydictionary = {"Rajkumar":1,"apple":2,True:3,"Apple":4,2.5:5,None:6}
# printing the dictionary before deleting
print(mydictionary)
# delete the dictionary
del mydictionary
# printing the dictionary after deleting
print(mydictionary){'Rajkumar': 1, 'apple': 2, True: 3, 'Apple': 4, 2.5: 5, None: 6}
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
C:\Users\RAJKUM~1\AppData\Local\Temp/ipykernel_14124/2734959277.py in <module>
9
10 # # printing the dictionary after deleting
---> 11 print(mydictionary)
NameError: name 'mydictionary' is not defined
Iterating a Dictionary in Python
We can iterate a dictionary in Python using for-loop and while-loop .
Example 1:
# for loop with dictionary as iterator
mydictionary = {"Rajkumar":1,"apple":2,True:3,"Apple":4,2.5:5,None:6}
for element in mydictionary:
print(element)Rajkumar apple True Apple 2.5 None
In the above code we have iterated all element from mydictionary using for-loop . By default it will print all the key . To print the value we need to write mydictionary[element] instead of element in 4th line .
Example 2:
# python while loop with dictionary datatype
mydictionary = {"Rajkumar":1,"apple":2,True:3,"Apple":4,2.5:5,None:6}
number=0
while number < len(mydictionary):
print(list(mydictionary.keys())[number])
number+=1Rajkumar apple True Apple 2.5 None
In the above code we have iterated all keys from mydictionary using while-loop . Here using list(mydictionary.keys()) we have converted {"Rajkumar":1, "apple":2, True:3, "Apple":4, 2.5:5, None:6} to ["Rajkumar","apple",True,"Apple",2.5,None]
To know about len() function click here .
Nested Dictionary in Python
When we use dictionary inside a dictionary then it is called Nested dictionary . Earlier we have seen that dictionary items can be of any datatype . So dictionary item can be a dictionary .
Example :
# nested dictionary in python
mydictionary = {"Rajkumar":1,"apple":2,True:3,"Apple":{"mango":1,"banana":2},2.5:5,None:6}
print(mydictionary){'Rajkumar': 1, 'apple': 2, True: 3, 'Apple': {'mango': 1, 'banana': 2}, 2.5: 5, None: 6}
In the above code we have seen that Python accepts a dictionary as dictionary value .
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