No Fluff Guide to Python - P7 - Dictionary
Dictionary
- Imagine you have a phone book.
- You can look up a person's name
- find their phone number.
- You can also add new people to the phone book
- remove people from the phone book.
A Python dictionary is like a phone book.
- You can store any kind of data in a dictionary
- like names, phone numbers, and addresses.
- You can also access the data in a dictionary using a key.
- To create a dictionary, you use the
{}curly braces. - Structured in a Key Value pair
- "Key": "Value"
Create a dictionary, name and age
dict = {
"name" : "vish",
"age" : 30
} Key: Value
Keys = IDs
animals = {
"cat": "meow",
"dog": "woof",
"duck": "quack",
"chicken": "cluck"
"chicken": "click" ❌
}
#Dictionary keys do not allow duplicates
You can access any particular value:
print(animals['duck'])Output: quack
Print all keys:
dict1={"key1":1,"key2":"value2",3:"value3"}
print(dict1.keys())
# all the keys are printed
Output:dict_keys(['key1', 'key2', 3])
Print all values:
print(dict1.values())
# all the values are printedOutput:
dict_values([1, 'value2', 'value3'])
Check Existence:
- in operator
- check if a key is in a dictionary
dict = {
"name" : "vish",
"age" : 30
}
if "name" in my_dict:
print("The key 'name' exists in the dictionary.")
if "job" in my_dict:
print("The key 'job' does not exist in the dictionary.")in operator works for Lists, sets and strings too:
my_list = [1, 2, 3, 4, 5]
if 3 in my_list:
print("The element 3 exists in the list.")
my_set = {1, 2, 3, 4, 5}
if 3 in my_set:
print("The element 3 exists in the set.")
String:
my_string = "Do one thing every day that scares you.!" if "one" in my_string: print("The substring 'one' exists in the string.")
Updates:
dict1["key1"]="replace_one"
# value assigned to key1 is replaced
print(dict1)
#Output
#{'key1': 'replace_one', 'key2': 'value2', 3: 'value3'} print(dict1["key1"])
#Output
#replace_one
dict1={
"fruit1":"apple",
"fruit2":"banana",
"veg1":"tomato"
}
dict1.update({"veg2":"chilli"})
# updates the dictionary at the end
print(dict1)
#Output
#{
'fruit1': 'apple',
'fruit2': 'banana',
'veg1': 'tomato',
'veg2': 'chilli'
}
dict1.pop("veg2")
print(dict1)
#Output
#{
'fruit1': 'apple',
'fruit2': 'banana',
'veg1': 'tomato'
}
Nested Dictionaries
- Dictionary within another dictionary
- useful for organizing data into hierarchical structure
- example:
- Dictionary of countries containing
- dictionary of cities
countries = {
"USA": {
"capital": "Washington, D.C.",
"population": 332000000,
},
"Canada": {
"capital": "Ottawa",
"population": 38000000,
},
}
To access the value of a key in a nested dictionary, you can use the square brackets ([]) operator multiple times. For example, the following code prints the capital city of the USA:
print(countries["USA"]["capital"])
List of Dictionaries
- a list containing dictionaries
- storing related information
- example:
- list of all students
- each represented by a dictionary of related info
students = [
{
"name": "Her",
"age": 20,
"gpa": 3.5,
},
{
"name": "Him",
"age": 21,
"gpa": 3.8,
},
]To access the value of a key in a dictionary in a list of dictionaries, you can use the square brackets ([]) operator twice. For example, the following code prints the name of the first student in the list:
print(students[0]["name"])
Dictionaries of Lists
- dictionary that maps Keys: Lists
- useful for storing collection of related data items
- organized into groups
- Dictionary of all countries
- list of languages spoken
countries = {
"India": ["Hindi", "English"],
"USA": ["English", "Spanish"],
"China": ["Mandarin", "Cantonese"],
"Japan": ["Japanese", "English"],
}To access the value of a key in a dictionary of lists, you can use the square brackets ([]) operator twice. For example, the following code prints the list of languages in India:
print(countries["India"])Real-world examples
In a social media platform, a dictionary can be used to store the posts of a user. The keys can be the post IDs and the values can be the post content.
Storing User Posts:
Each user's posts can be stored in a dictionary, where the keys are the post IDs and the values are the post content. This allows the platform to efficiently retrieve and display a user's posts when they visit their profile or when their posts appear in their friends' feeds.
user_posts = {
"post_1": {
"content": "I'm having a great time at the beach!",
"timestamp": "2023-08-22T14:30:00Z",
"likes": 100,
"comments": [
{
"author": "Amit",
"content": "Nice photo!"
},
{
"author": "Radhe",
"content": "I wish I was there!"
},
]
},
"post_2": {
"content": "Just finished reading a great book!",
"timestamp": "2023-08-20T10:00:00Z",
"likes": 50,
"comments": [
{
"author": "Mohan",
"content": "What book is it?"
},
{
"author": "Rakesh",
"content": "I've heard good things about that book!"
},
]
},
}Storing User Profiles:
Each user's profile information can also be stored in a dictionary, where the keys are the user IDs and the values are the profile information. This information can include the user's name, profile picture, bio, and other relevant details.
user_profiles = {
"user_1": {
"name": "John Doe",
"profile_picture": "profile_picture.jpg",
"bio": "I'm a software engineer and I love to travel.",
"friends": ["user_2", "user_3"],
},
"user_2": {
"name": "Jane Smith",
"profile_picture": "profile_picture.png",
"bio": "I'm a marketing manager and I love to cook.",
"friends": ["user_1", "user_3"],
},
"user_3": {
"name": "Michael Jones",
"profile_picture": "profile_picture.gif",
"bio": "I'm a graphic designer and I love to play video games.",
"friends": ["user_1", "user_2"],
},
}
Sorting the Dictionary:
- We have a dictionary called iphones that
- contains information about different iPhone models.
- Each model has two keys:
- width and height
- which represent the width and height of the phone's screen in pixels.
iphones = {
"iPhone 12": {
"width": 828,
"height": 1792
},
"iPhone 12 mini": {
"width": 750,
"height": 1542
},
"iPhone 11 Pro Max": {
"width": 1242,
"height": 2688
}
}
};To sort the dictionary by the width key, we can use the sorted() function. The sorted() function takes a list or dictionary as its first argument and a key function as its second argument. The key function is used to extract the value that we want to sort by from each element in the list or dictionary.
sorted_iphones = sorted(iphones, key=lambda x: iphones[x]["width"])
print(sorted_iphones)Output:['iPhone 12 mini', 'iPhone 12', 'iPhone 11 Pro Max']
The lambda function
- used to define the key function.
- takes one argument, phone
- which represents each element in the iphones dictionary.
- Inside the lambda function,
- we use the
phone["width"]expression - to extract the width value from the
phonedictionary. - The sorted() function will return a new list of tuples
- where each tuple contains a key-value pair from the iphones dictionary.
- The tuples will be sorted in ascending order based on the width value.
Dictionary Iteration:
You can then use these names to traverse the original Dictionary.
for phone in sorted_iphones:
print(iphones[phone])
Output:
{'width': 750, 'height': 1542}
{'width': 828, 'height': 1792}
{'width': 1242, 'height': 2688}
animals = {
"cat": "meow",
"dog": "woof",
"duck": "quack",
"chicken": "cluck"
}
for key, value in animals.items():
print(key + " does " + value)Output:
cat does meow
dog does woof
duck does quack
chicken does cluck
For these simple dictionaries, you can sort them directly using sorted()
animals = {
"cat": "meow",
"dog": "woof",
"duck": "quack",
"chicken": "cluck"
}
for name in sorted(animals.keys()):
print(name )Output:
cat
chicken
dog
duck
That covers all the most important tasks related to dictionary.
Until Next Time!!
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