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In this article, we will discuss dictionaries in Python.

What is Dictionary?

Dictionary is defined in key and value format {key : value}. In Dictionary each key is separated from its value by a colon (:), the items are separated by commas, and the whole thing is enclosed in curly braces. An empty dictionary without any items is written with just two curly braces, like this: {}. Keys are unique within a dictionary while values may not be. The values of a dictionary can be of any type, but the keys must be of an immutable data type such as strings, numbers, or tuples.

# dictionary in python

d1={}
print(type(d1))  #<class 'dict'>


d2=dict()
print(type(d2))  # <class 'dict'>

Properties

• Keys must be immutable datatypes that means you can use strings, numbers or tuples as dictionary keys.
• More than one entry per key not allowed. Which means no duplicate key is allowed.When duplicate keys encountered during assignment, the last assignment wins.

Accessing value

In dictionary we use keys to access that particular value as shown.

student={"name": "rahul","age":20,"gender":"male"}

# to access each element we use key
print("name of student is: ",student["name"])
print("age of student is: ",student["age"])

Output

name of student is: rahul

age of student is: 20

if key is not present than key error occurs as shown below:

student={"name": "rahul","age":20,"gender":"male"}

# to access each element we use key
print("name of student is: ",student["name"])
print("age of student is: ",student["age"])
print("email of student is: ",student["email"])

Output

name of student is: rahul

age of student is: 20

Traceback (most recent call last): File "c:/Users/meenu garg/Desktop/Python/PythonCodes/datatype/dictionary.py", line 13, in print("email of student is: ",student["email"]) KeyError: 'email'

Updating Dictionary

We can update a dictionary by adding a new entry or a key-value pair, modifying an existing entry, or deleting an existing entry as shown below in the simple example:

student={"name": "rahul","age":20,"gender":"male"}
# updating email
student['email']="rahul@gmail.com"

# to access each element we use key
print("name of student is: ",student["name"])
print("age of student is: ",student["age"])
print("email of student is: ",student["email"])

Output

name of student is: rahul

age of student is: 20

email of student is: rahul@gmail.com

Accessing Keys

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

print(stu.keys())

Output

dict_keys(['name', 'age', 'courses'])

Accessing Values

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

print(stu.values())

Output

dict_values(['John Doe', 15, ['Python', 'Django']])

Accessing Items

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

print(stu.items())

Output

dict_items([('name', 'John Doe'), ('age', 15), ('courses', ['Python', 'Django'])])

Iterating the dictionary

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

for k, v  in stu.items():
    print(f'key is {k} ---> value is {v}')

Output

key is name ---> value is John Doe

key is age ---> value is 15

key is courses ---> value is ['Python', 'Django']

get method

dictionary_name.get(key_name)
dictionary_name.get(key_name , return_statement)

get(key_name) method fetches value against a key. If key is not present then it returns None, also we could provide a custom return statement.

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

print(stu.get('age'))
print(stu.get('gender'))

print(stu.get('gender' , 'it is not present')

Output

15

None

it is not present

pop method

It pops out the key, value by passing key name as parameter.

Syntax

dictionary_name.pop(key_name)

Example

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

print("BEFORE: ",stu)
stu.pop('age')
print("AFTER: ",stu)

Output BEFORE: {'name': 'John Doe', 'age': 15, 'courses': ['Python', 'Django']}

AFTER: {'name': 'John Doe', 'courses': ['Python', 'Django']}

popitem method

popitem method pops out last element from the dictionary.

Syntax

dictionary_name.popitem()

Example

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

print("BEFORE: ",stu)
stu.popitem()
print("AFTER: ",stu)

Output

BEFORE: {'name': 'John Doe', 'age': 15, 'courses': ['Python', 'Django']}

AFTER: {'name': 'John Doe', 'age': 15}

Deleting Elements

We can also use del keyword to delete a particular key

Syntax

del dictionary_name[key]

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

del stu["age"]
print(stu["age"])

Output

Traceback (most recent call last): File "c:/Users/meenu garg/Desktop/Python/PythonCodes/datatype/dictionary.py", line 21, in print(student["age"]) KeyError: 'age'

Clearing out complete dictionary

Syntax

dictionary_name.clear()

stu = {
    'name' :"John Doe",
    'age' :15,
    'courses': ['Python','Django']
}

stu.clear()
print(student)

Output

{}

The End

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