Dictionary: dictionary methods and built-in functions

Dictionary: concept of key-value pair, creating, initializing, traversing, updating and deleting elements, dictionary methods and built-in functions – dict(), len(), keys(), values(), items(), update(), del, clear()

Class 11 Python: Dictionaries

Dictionaries are a versatile and powerful data structure in Python used to store data in key-value pairs. Each key is unique, and it maps to a specific value.

1. Concept of Key-Value Pair

A dictionary in Python consists of keys and values:

Key: A unique identifier for the value.
Value: The data associated with the key.

Example:

student = {
    "name": "Alice",
    "age": 17,
    "grade": "A"
}

2. Creating and Initializing Dictionaries

Creating an Empty Dictionary:
```
my_dict = {}
```

Creating a Dictionary with Initial Values:

student = {
    "name": "Alice",
    "age": 17,
    "grade": "A"
}

Using the dict() Constructor:

student = dict(name="Alice", age=17, grade="A")

Creating a Dictionary from a List of Tuples:

student = dict([("name", "Alice"), ("age", 17), ("grade", "A")])

3. Traversing Dictionaries

To access and print all key-value pairs in a dictionary:

Using a for Loop:

student = {"name": "Alice", "age": 17, "grade": "A"}
for key, value in student.items():
    print(f"{key}: {value}")

Using Dictionary Comprehension:

student = {"name": "Alice", "age": 17, "grade": "A"}
{key: value for key, value in student.items()}

4. Updating and Deleting Elements

Updating Elements: You can change the value associated with a key.

student = {"name": "Alice", "age": 17, "grade": "A"}
student["age"] = 18  # Update the age

Adding New Key-Value Pairs:

student = {"name": "Alice", "age": 17}
student["grade"] = "A"  # Add new key-value pair

Deleting Elements:

Using del Keyword:

student = {"name": "Alice", "age": 17, "grade": "A"}
del student["grade"]  # Remove the key-value pair with key "grade"

Using pop():


student = {"name": "Alice", "age": 17, "grade": "A"}
age = student.pop("age")  # Remove and return the value associated with "age"

Using popitem():

student = {"name": "Alice", "age": 17, "grade": "A"}
item = student.popitem()  # Remove and return the last key-value pair

Using clear():

student = {"name": "Alice", "age": 17, "grade": "A"}
student.clear()  # Remove all key-value pairs

5. Dictionary Methods and Built-in Functions

dict(): Constructor to create a dictionary.
```
d = dict(name="Alice", age=17)
```

len(): Returns the number of key-value pairs in the dictionary.

student = {"name": "Alice", "age": 17}
length = len(student)  # Output: 2

keys(): Returns a view object displaying a list of all keys.

student = {"name": "Alice", "age": 17}
keys = student.keys()  # Output: dict_keys(['name', 'age'])

values(): Returns a view object displaying a list of all values.

student = {"name": "Alice", "age": 17}
values = student.values()  # Output: dict_values(['Alice', 17])

items(): Returns a view object displaying a list of key-value tuple pairs.

student = {"name": "Alice", "age": 17}
items = student.items()  # Output: dict_items([('name', 'Alice'), ('age', 17)])

update(): Updates the dictionary with key-value pairs from another dictionary or iterable.
```
student = {"name": "Alice"}
student.update({"age": 17, "grade": "A"})
```

clear(): Removes all items from the dictionary.

student = {"name": "Alice", "age": 17}
student.clear()  # Results in {}

Summary

Dictionaries store data in key-value pairs.
Creating dictionaries can be done using literals, the dict() constructor, or from lists of tuples.
Traversing involves iterating through key-value pairs.
Updating and deleting involve modifying or removing key-value pairs.
Dictionary methods provide various ways to interact with the dictionary, including retrieving keys, values, and items, as well as updating and clearing the dictionary.