Python Dictionary

In python, dictionary is a collection of an unordered sequence of key-value pair items. In python, while storing the elements in the dictionary object,

you need to make sure that the keys are unique because the dictionary object will allow us to store duplicate values, but the keys must be unique.

?In python, you can create the dictionary by enclosing the key-value pair items in?key: value?form within the braces?{ }?and the key-value pair items must be separated by commas.

Following is the example of creating the dictionary with different key-value pair items in python.

# Dictionary with integer keys

a = {1:?30,?2:?20}

# Dictionary with string keys

b = {"Name":?"Ajith",?"Wife":?"Shalini"}

# Dictionary with mix types

c = {1:?"Welcome",?"Id":?10}

print("a = ", a)

print("b = ", b)

print("c = ", c)

If you observe the above example, we created different dictionary objects and printed the dictionary object items using the python print method.

When you execute the above python dictionary example, you will get the result as shown below.

a = {1: 30, 2: 20}

b = {'Name': 'Ajith', 'Wife’: 'Shalini'}

c = {1: 'Welcome', 'Id': 10}

Access Dictionary Items:

You can access dictionary elements in python, either using the key name inside square brackets?[ ]?or using the key name inside the?get()?method.

Following is the example of accessing the dictionary elements using key names inside square brackets in python.

dct = {"Id":?1,?"Name":?"Suresh",?"Location":?"Hyderabad"}

uid = dct["Id"]

name = dct["Name"]

location = dct["Location"]

print("Id = {}, Name = {}, Location = {}".format(uid, name, location))

If you observe the above example, we are accessing elements from the dictionary using different key names with square brackets?[ ].

The above python dictionary example will return the result as shown below.

Id = 1, Name = Suresh, Location = Hyderabad

In python, you can also use key names with the?get()?method to get or access the dictionary items.

Following is the example of accessing the elements from the dictionary using key names with?get()?method in python.

dct = {"Id":?1,?"Name":?"Suresh",?"Location":?"Hyderabad"}

uid = dct.get("Id")

name = dct.get("Name")

location = dct.get("Location")

print("Id = {}, Name = {}, Location = {}".format(uid, name, location))

The above python dictionary example will return the result like as shown below.

Id = 1, Name = Suresh, Location = Hyderabad

If you try to access the dictionary elements that do not exist with the specified key, you will get that item value as “None”.?

dct = {"Id":?1,?"Name":?"Suresh",?"Location":?"Hyderabad"}

uid = dct.get("Id1")

name = dct.get("Name1")

location = dct.get("Location1")

print("Id = {}, Name = {}, Location = {}".format(uid, name, location))

The above dictionary example will return the result like as shown below.

Id = None, Name = None, Location = None

Change Dictionary Item Values:

Using key values, you can change or update the value of the required item in the dictionary.

Following is the example of changing the dictionary item values using keys in python.

dct = {"Id":?1,?"Name":?"Suresh",?"Location":?"Hyderabad"}

print("Before: ",dct)

dct["Id"] =?10

dct["Name"] =?"Rohini"

dct["Location"] =?"Guntur"

print("After: ",dct)

When you execute the above python dictionary example, you will get the result as shown below.

Before: {'Id': 1, 'Name': 'Suresh', 'Location': 'Hyderabad'}

After: {'Id': 10, 'Name': 'Rohini', 'Location': 'Guntur'}

Add Items to Dictionary:

In python, you can add items to the dictionary by assigning a value to the new keys.

Following is the example of adding items to the dictionary using new keys in python.

mbl = {"Brand":?"Oneplus",?"Model":?"8T"}

print("Before: ",mbl)

mbl["Color"] =?"Aqua"

mbl["Type"] =?"5G"

print("After: ",mbl)

The above python dictionary example will return the result as shown below.

Before: {'Brand': 'Oneplus', 'Model': '8T'}

After: {'Brand': 'Oneplus', 'Model': '8T', 'Color': 'Aqua', 'Type': '5G'}

Remove Items from Dictionary:

In python, you can delete/remove items from dictionary object using either?del?keyword,?pop(),?popitem(), or?clear()?methods based on our

requirements.

The del keyword is useful for removing dictionary items with the specified key name or deleting the dictionary completely.

Following is the example of using the?del?keyword to delete the dictionary items with the specified key names in python.

mbl = {"Brand":?"Oneplus",?"Model":?"8T",?"Color":?"Aqua",?"Type":?"5G"}

print("Before: ",mbl)

del?mbl["Color"]

del?mbl["Type"]

print("After: ",mbl)

The above python dictionary example will return the result as shown below.

Before: {'Brand': 'Oneplus', 'Model': '8T', 'Color': 'Aqua', 'Type': '5G'}

After: {'Brand': 'Oneplus', 'Model': '8T'}

If required, you can also delete the complete dictionary using?del?keyword in python.

mbl = {"Brand":?"Oneplus",?"Model":?"8T",?"Color":?"Aqua"}

del?mbl

print("After: ",mbl)

If you observe the above example, we are deleting the complete list using the?del?keyword and trying to print the list. The above example will return

the result as shown below.

Traceback (most recent call last):

? File "D:\pythondic.py", line 4, in <module>

??? print("After: ",mbl)

NameError: name 'mbl' is not defined

We got an exception because we tried to print the dictionary (mbl) that is already deleted.

In python, the dictionary?pop()?method is useful to remove the dictionary items based on the specified key name.

Following is the example of using the dictionary?pop()?method to remove the dictionary items.

mbl = {"Brand":?"Oneplus",?"Model":?"8T",?"Color":?"Aqua",?"Type":?"5G"}

print("Before: ",mbl)

mbl.pop("Color")

mbl.pop("Type")

print("After: ",mbl)

When you execute the above python dictionary program, you will get the result as shown below.

Before: {'Brand': 'Oneplus', 'Model': '8T', 'Color': 'Aqua', 'Type': '5G'}

After: {'Brand': 'Oneplus', 'Model': '8T'}

Instead of using dictionary keys, you can use?popitem()?method in python to delete or remove the last inserted item.?

mbl = {"Brand":?"Oneplus",?"Model":?"8T",?"Color":?"Aqua"}

print("Before: ",mbl)

mbl.popitem()

print("After: ",mbl)

The above python dictionary example will return the result as shown below.

Before: {'Brand': 'Oneplus', 'Model': '8T', 'Color': 'Aqua'}

After: {'Brand': 'Oneplus', 'Model': '8T'}

If you want to clear or empty dictionary items, you can use the dictionary?clear()?method.

Following is the example of removing all the dictionary items using the?clear()?method in python.

mbl = {"Brand":?"Oneplus",?"Model":?"8T",?"Color":?"Aqua"}

print("Before: ",mbl)

mbl.clear()

print("After: ",mbl)

The above python dictionary example will return the result as shown below.

Before: {'Brand': 'Oneplus', 'Model': '8T', 'Color': 'Aqua'}

After: {}

Dictionary Length:

In python, to count the number of items (key-value pairs) in the list, use the?len()?function.

Following is the example of using?len()?function in python to get the dictionary length/size.

mbl = {"Brand":?"Oneplus",?"Model":?"8T",?"Color":?"Aqua"}

print("Dictionary Size: ",?len(mbl))?#Dictionary Size: 3

By using?len()?function, you can also check whether the dictionary is empty or not like as shown below.?

mbl = {}

count =?len(mbl)

if?count >?0:

? ?print("Dictionary size: ", count)

else:

? ??print("Dictionary is empty")

The above dictionary example will return the result as shown below.

Dictionary is empty

Join or Concatenate Dictionaries:

You can use an?update()?method to join or merge multiple dictionaries with all the list elements in python.

Following is the example of joining the dictionaries using the?update()?method in python.

dct1 = {1:?10,?2:?20}

dct2 = {"name":?"suresh",?"location":?"guntur"}

dct1.update(dct2)

print(dct1)

The above list example will return the result as shown below.

{1: 10, 2: 20, 'name': 'suresh', 'location': 'guntur'}

If two dictionaries (dct1,?dct2) have the same keys, the?update()?method will consider using the values of the second dictionary (dct2).

Following is the example of merging the two dictionaries with the same keys using the?update()?method in python.

dct1 = {1:?10,?2:?20,?"location":?"guntur"}

dct2 = {1:?30,?"name":?"suresh",?"location":?"guntur"}

dct1.update(dct2)

print(dct1)

The above dictionary example will return the result as shown below.

{1: 30, 2: 20, 'location': 'guntur', 'name': 'suresh'}

Check If Dictionary has Key:

By using?in?and?not in?operators, you can check whether the specified key exists in the dictionary or not.

Following is the example to verify whether the dictionary has specified keys or not using?in?operator in python.

dct = {1:?10,?"name":?"suresh",?"location":?"guntur"}

print("1 in dict: ",?1?in?dct)

print("name in dict: ",?"name"?in?dct)

print("50 in dict: ",?50?in?dct)

The above dictionary example will return the result as shown below.

1 in dict: True

name in dict: True

50 in dict: False

Python Iterate through Dictionary:

By using?for loop, you can iterate through the items of the dictionary in python. While iterating over dictionary items, it will return only the keys of the dictionary.

Following is the example of looping through the dictionary items in python to get all dictionary keys using?for loop.

dct = {1:?10,?"name":?"suresh",?"location":?"guntur"}

for?item?in?dct:

? ??print(item)

The above dictionary example will return the result as shown below.

1

name

location

If you want to get all the dictionary values, you need to use the dictionary object's key names, as shown below.

dct = {1:?10,?"name":?"suresh",?"location":?"guntur"}

for?item?in?dct:

? ??print(dct[item])

The above dictionary example will return the result as shown below.

10

suresh

guntur

Python Copy Dictionary:

In python, you can copy a dictionary either using the dictionary?copy()?method or?dict()?method, but copying the dictionary like?dic2 = dic1?is not allowed because the?dic2?will reference?dic1. So, the changes you made in?dic1?will automatically reflect in?dic2.

Following is the example of using the dictionary?copy()?method to copy a dictionary in python.?

dic1 = {1:?10,?"name":?"suresh",?"location":?"guntur"}

dic2 = {}

print("====Before Copy====")

print("Dict1: ", dic1)

print("Dict2: ", dic2)

dic2 = dic1.copy()

print("====After Copy====")

print("Dict1: ", dic1)

print("Dict2: ", dic2)

The above dictionary example will return the result as shown below.

?

====Before Copy====

Dict1: {1: 10, 'name': 'suresh', 'location': 'guntur'}

Dict2: {}

====After Copy====

Dict1: {1: 10, 'name': 'suresh', 'location': 'guntur'}

Dict2: {1: 10, 'name': 'suresh', 'location': 'guntur'}

Following is the example of using the built-in?dict()?method to copy a dictionary in python.

dic1 = {1:?10,?"name":?"suresh",?"location":?"guntur"}

dic2 = {}

print("====Before Copy====")

print("Dict1: ", dic1)

print("Dict2: ", dic2)

dic2 =?dict(dic1)

print("====After Copy====")

print("Dict1: ", dic1)

print("Dict2: ", dic2)

The above dictionary example will return the result as shown below.

====Before Copy====

Dict1: {1: 10, 'name': 'suresh', 'location': 'guntur'}

Dict2: {}

====After Copy====

Dict1: {1: 10, 'name': 'suresh', 'location': 'guntur'}

Dict2: {1: 10, 'name': 'suresh', 'location': 'guntur'}

Python Nested Dictionary:

In python, you can create a nested dictionary by adding one dictionary inside of another dictionary.

Following is the example of creating the nested dictionary in python.

cars = {

? ??"car1": {

? ? ? ??"brand":?"hyundai",

? ? ? ??"name":?"i10"

? ? ? ? },

? ??"car2": {

? ? ? ??"brand":?"kia",

? ? ? ??"name":?"sonet"

? ? ? ?}

? ? }

print(cars)

The above dictionary example will return the result as shown below.

{'car1': {'brand': 'hyundai', 'name': 'i10'}, 'car2': {'brand': 'kia', 'name': 'sonet'}}

If you want, you can also create a nested dictionary, as shown below.

car1 = {"brand":?"hyundai",?"name":?"i10"}

car2 = {"brand":?"kia",?"name":?"sonet"}

cars = {

? ??"car1": car1,

? ??"car2": car2

? ? }

print(cars)

Python Sort Dictionary Elements:

In python, the?sorted()?method will sort the dictionary elements based on the keys and values. By default, the?sorted()?method will sort the list elements in ascending order.

Following is the example of sorting the dictionary elements in ascending order using keys in the?sorted()?method.

dct = {4:?10,?1:?20,?5:?30,?3:?60}

# print sorted dictionary keys

print(sorted(dct.keys()))

# print sorted dictionary items

print(sorted(dct.items()))

The above dictionary example will return the result as shown below.

[1, 3, 4, 5]

[(1, 20), (3, 60), (4, 10), (5, 30)]

Following is the example of sorting the dictionary elements in ascending order using values in the?sorted()?method.?

dct = {4:?10,?1:?20,?5:?30,?3:?60}

# print sorted dictionary values

print(sorted(dct.values()))

The above dictionary example will return the result as shown below.

[10, 20, 30, 60]

To sort the dictionary elements in descending order, you need to use the optional?reverse = True?property with?sorted()?method like as shown below.

dct = {4:?10,?1:?20,?5:?30,?3:?60}

# print sorted dictionary keys

print(sorted(dct.keys(), reverse = True))

# print sorted dictionary items

print(sorted(dct.items(), reverse = True))

The above dictionary example will return the result as shown below.

[5, 4, 3, 1]

[(5, 30), (4, 10), (3, 60), (1, 20)]

To sort dictionary items either in ascending or descending order, you need to make sure that all the dictionary keys/values must be the same type;

otherwise, you will get a?TypeError?exception.

dct = {4:?10,?1:?20,?"name":?"suresh",?"location":?"guntur"}

# print sorted dictionary keys

print(sorted(dct.keys(), reverse = True))

# print sorted dictionary values

print(sorted(dct.values(), reverse = True))

The above python dictionary example will return the result as shown below.

Traceback (most recent call last):

? File "D:\pythondict.py", line 2, in <module>

??? for item in sorted (dic):

TypeError: '<' not supported between instances of 'str' and 'int'

Python Dictionary Methods:

In python, the dictionary object has a set of built-in methods to perform different operations like adding items to the dictionary, removing elements from

the dictionary, etc., based on your requirements.

Following are the built-in dictionary functions available in the python programming language.

get() - It is useful to get the value of the specified key.

items() - It will return a list with key-value pairs.

keys() - It will return the list of all the keys in the dictionary.

fromkeys() - It will return the dictionary with the specified keys.

values() - It will return the list of all the values in the dictionary.

pop() - It is useful to remove the element at the specified key.

popitem() - It will remove the last inserted element.

clear() - It is useful to remove all the elements of a dictionary.

update() - It will update the dictionary with the specified key-value pairs.

copy() - It is useful to return a copy of the dictionary.

setdefault() - It will return the value of the specified key. If the key is not found, the default value will be returned.