Merge pull request #1095 from AmrutaJayanti/Dec

Create Decorators-Lambda-Functions.md

Author: ajay-dhangar

docs/python/Decorators-Lambda-Functions.md

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+# Decorators 
+
+Decorators in Python are a powerful and flexible feature that allows you to modify or enhance the behavior of functions or classes. They are essentially functions that wrap other functions or methods, allowing you to add functionality before, after, or around the original function's behavior.
+
+#### Syntax 
+
+Decorators use the `@decorator_name` syntax above the function definition.
+
+### Types of Decorators 
+
+**1. Built-in  Function Decorators**
+
+- `@staticmethod`: Defines a method that does not operate on an instance of the class or modify its state.
+- `@classmethod`: Defines a method that operates on the class itself, rather than an instance.
+- `@property`: Allows you to define methods in a class that can be accessed like attributes.
+
+```python
+class MyClass:
+    def __init__(self, value):
+        self._value = value
+
+    @property
+    def value(self):
+        return self._value
+
+    @value.setter
+    def value(self, new_value):
+        self._value = new_value
+
+    @staticmethod
+    def static_method():
+        print("This is a static method.")
+
+    @classmethod
+    def class_method(cls):
+        print("This is a class method.")
+```
+
+**2. Custom Function Decorators:**
+
+- Simple Function Decorators : Adds functionality to a function.
+  ```python
+  def my_decorator(func):
+    def wrapper():
+        print("Something is happening before the function is called.")
+        func()
+        print("Something is happening after the function is called.")
+    return wrapper
+
+   @my_decorator
+   def say_hello():
+     print("Hello!")
+
+   say_hello()
+  ```
+- Decorator with Arguments: Takes arguments to modify the behavior.
+  ```python
+  def repeat(num_times):
+    def decorator_repeat(func):
+        def wrapper(*args, **kwargs):
+            for _ in range(num_times):
+                result = func(*args, **kwargs)
+            return result
+        return wrapper
+    return decorator_repeat
+
+  @repeat(num_times=3)
+  def greet(name):
+    print(f"Hello {name}")
+
+  greet("Alice")
+  ```
+Here, `*args` and `**kwargs` are special syntax in Python that allow a function to accept an arbitrary number of positional and keyword arguments.
+
+**3. Class Decorators:**
+
+Instead of taking functions as the decorators , here we use the class definition as the decorator.
+
+```python
+def class_decorator(cls):
+    class Wrapped(cls):
+        def new_method(self):
+            return "New Method"
+    return Wrapped
+
+@class_decorator
+class MyClass:
+    def original_method(self):
+        return "Original Method"
+
+instance = MyClass()
+print(instance.original_method())
+print(instance.new_method())
+```
+
+### Decorators Chaining
+
+You can apply multiple decorators to a single function. Decorators are applied from bottom to top.
+
+```python
+def decorator1(func):
+    def wrapper():
+        print("Decorator 1")
+        func()
+    return wrapper
+
+def decorator2(func):
+    def wrapper():
+        print("Decorator 2")
+        func()
+    return wrapper
+
+@decorator1
+@decorator2
+def my_function():
+    print("Hello!")
+
+my_function()
+```
+
+
+# Lambda Functions
+
+Lambda functions in Python, also known as anonymous functions, are small, unnamed functions defined using the `lambda` keyword.
+
+#### Syntax 
+
+```python
+lambda arguments: expression
+```
+
+#### Example: 
+
+```python
+from functools import reduce
+
+numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+
+# Filter even numbers, square them, and then find their product
+even_squares_product = reduce(
+    lambda x, y: x * y,
+    map(lambda x: x**2, filter(lambda x: x % 2 == 0, numbers))
+)
+
+print(even_squares_product)  # Output: 64 * 16 * 36 * 100 = 3686400
+```
+
+
+