Day-20,21 added

Author: Dark-Vinaal

Day-20/notes.md

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+# Day 20 – Dictionary in Python
+
+## 🎯 Topics Covered
+
+- Dictionary
+  - `dict()`
+  - `get()`
+  - `update()`
+  - `pop()`
+  - `popitem()`
+  - `clear()`
+  - `items()`
+  - `keys()`
+  - `values()`
+
+---
+
+# What is a Dictionary?
+
+- A dictionary in Python is an unordered, mutable, and indexed collection of key–value pairs.
+It is used to store data values like a real-world dictionary — where each key maps to a specific value.
+
+# Example:
+```python
+student = {"name": "Vinaal", "age": 21, "course": "Python"}
+print(student)
+```
+
+---
+
+## Creating a Dictionary
+
+You can create a dictionary using curly braces {} or the dict() constructor.
+
+---
+
+## Using curly braces
+```python
+info = {"brand": "Tesla", "model": "Model X", "year": 2025}
+```
+
+## Using dict() constructor
+```python
+data = dict(name="Dark AI", skill="Full Stack Developer")
+```
+
+---
+
+## Accessing Dictionary Elements
+
+### Using Key
+```python
+person = {"name": "Alice", "age": 25}
+print(person["name"])   # Output: Alice
+```
+
+### Using get()
+
+- Safely returns the value of a key. If the key doesn’t exist, it returns None instead of an error.
+```python
+person = {"name": "Alice", "age": 25}
+print(person.get("age"))       # Output: 25
+print(person.get("city"))      # Output: None
+```
+
+### Modifying Dictionary Elements
+
+- You can update an existing key or add a new one.
+```python
+car = {"brand": "BMW", "year": 2020}
+car["year"] = 2025     # Update value
+car["color"] = "Black" # Add new key-value pair
+print(car)
+```
+
+---
+
+## Dictionary Methods
+
+### keys()
+
+- Returns all keys from the dictionary.
+```python
+person = {"name": "Vinaal", "age": 21, "course": "Python"}
+print(person.keys())
+```
+
+### Output
+```python
+dict_keys(['name', 'age', 'course'])
+```
+
+### values()
+
+- Returns all values from the dictionary.
+```python
+person = {"name": "Vinaal", "age": 21}
+print(person.values())
+```
+
+### Output
+```python
+dict_values(['Vinaal', 21])
+```
+
+### items()
+
+- Returns all key–value pairs as tuples.
+```python
+person = {"name": "Vinaal", "age": 21}
+print(person.items())
+```
+
+### Output
+```python
+dict_items([('name', 'Vinaal'), ('age', 21)])
+```
+
+### update()
+
+- Merges another dictionary or adds new key–value pairs.
+```python
+student = {"name": "Dark", "age": 20}
+student.update({"age": 21, "course": "Python"})
+print(student)
+```
+
+### Output
+```python
+{'name': 'Dark', 'age': 21, 'course': 'Python'}
+```
+
+### pop()
+
+- Removes a specific key and returns its value.
+```python
+data = {"x": 10, "y": 20, "z": 30}
+data.pop("y")
+print(data)
+```
+
+### Output
+```python
+{'x': 10, 'z': 30}
+```
+
+### popitem()
+
+- Removes the last inserted key–value pair.
+```python
+info = {"a": 1, "b": 2, "c": 3}
+info.popitem()
+print(info)
+```
+
+### Output
+```python
+{'a': 1, 'b': 2}
+```
+
+### clear()
+
+- Removes all items from the dictionary.
+```python
+info = {"x": 100, "y": 200}
+info.clear()
+print(info)
+```
+
+### Output
+```python
+{}
+```
+
+---
+
+## Looping Through a Dictionary
+```python
+# Looping through keys:
+car = {"brand": "Tesla", "model": "S", "year": 2025}
+for key in car:
+    print(key)
+
+Looping through values:
+for value in car.values():
+    print(value)
+
+Looping through both keys and values:
+for key, value in car.items():
+    print(key, ":", value)
+```
+
+---
+
+## Copying a Dictionary
+
+- You can use copy() to make a duplicate dictionary.
+```python
+original = {"name": "Dark", "lang": "Python"}
+duplicate = original.copy()
+print(duplicate)
+```
+
+---
+
+## Nested Dictionary
+
+- A dictionary inside another dictionary.
+```python
+students = {
+    "student1": {"name": "Alice", "age": 20},
+    "student2": {"name": "Bob", "age": 22}
+}
+
+print(students["student1"]["name"])
+# Output: Alice
+```
+
+---
+
+## Built-in Functions for Dictionary
+```python
+len()   # Returns total number of key-value pairs
+str()   # Converts dictionary into a string
+type()  # Returns the type of the object
+```
+
+---
+
+## 📘 *Next step (Day 20):*  
+
+I’ll explore **Function**.

Day-21/notes.md

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+# Day 21 – Functions and Arguments in Python
+
+## 🔹 What is a Function?
+
+- A function is a block of reusable code that performs a specific task.
+It helps make programs more modular, readable, and reduces repetition.
+
+### Syntax:
+```python
+def function_name(parameters):
+    # block of code
+    return value
+```
+
+### Example:
+```python
+def greet():
+    print("Hello, welcome to Python learning!")
+```
+
+#### To call the function:
+
+`greet()`
+
+---
+
+### 🔹 Why Use Functions?
+
+- Increases code reusability.
+- Makes code modular and organized.
+- Easy to debug and maintain.
+- Avoids repetition of logic.
+
+---
+
+## Types of Arguments in Python Functions
+
+- Python supports multiple types of arguments to make functions flexible and powerful.
+
+---
+
+### 1. Positional Arguments
+
+- Arguments passed in the same order as defined in the function.
+```python
+def student(name, age):
+    print("Name:", name)
+    print("Age:", age)
+
+student("Vinaal", 21)
+```
+
+### Output:
+```python
+Name: Vinaal
+Age: 21
+```
+
+> ⚠️ The order matters — if you swap them, values will mismatch.
+
+---
+
+### 2. Default Arguments
+
+- A parameter can have a default value which is used if no argument is provided.
+```python
+def greet(name="User"):
+    print("Hello,", name)
+
+greet("Dark AI")
+greet()
+```
+
+### Output:
+```python
+Hello, Dark AI
+Hello, User
+```
+
+---
+
+### 3. Keyword Arguments
+
+- You can specify arguments by their parameter names, regardless of order.
+```python
+def display(name, age):
+    print(f"Name: {name}, Age: {age}")
+
+display(age=22, name="TechnoSport")
+```
+
+### Output:
+```python
+Name: TechnoSport, Age: 22
+```
+
+---
+
+### 4. Variable-Length (Arbitrary) Arguments
+
+- When you don’t know how many arguments will be passed, use:
+- *args → for non-keyworded variable arguments (tuple)
+
+#### Using *args
+```python
+def add_numbers(*args):
+    print("Numbers:", args)
+    print("Sum:", sum(args))
+
+add_numbers(10, 20, 30)
+```
+
+### Output:
+```python
+Numbers: (10, 20, 30)
+Sum: 60
+```
+
+---
+
+## Return Statement
+
+- The return keyword sends a result back to the caller.
+```python
+def multiply(a, b):
+    return a * b
+
+result = multiply(5, 3)
+print("Result:", result)
+```
+
+### Output:
+```python
+Result: 15
+```
+
+---
+
+## 📘 *Next step (Day 20):*  
+
+I’ll explore **Advanced Functions**.