﻿ Understanding Python Decorators
• author: selfedu

# Understanding Python Decorators

Python decorators are functions that take another function as an argument and extend its functionality. This article will explain how to define and use Python decorators with an example of the Euclidean algorithm, which finds the greatest common divisor of two natural numbers.

## Example: The Euclidean Algorithm

On one of our previous classes, we programmed the Euclidean algorithm to find the greatest common divisor of two natural numbers, a and b. The algorithm is defined as follows:

``````def euclidean_algorithm(a,b):
while b!=0:
temp = b
b = a % b
a = temp
return a
``````

Now, let's say we want to create a test to measure the speed of this function. We can implement this test by using a decorator function, as shown below.

## Creating a Test with a Decorator

To create a test with a decorator, we define a function called `test_time` that takes another function as an argument. We can create a wrapper function inside `test_time` that will compute the time it takes to execute the function and print the results to the console. Here's how it looks:

``````import time

def test_time(fn):
def wrapper(*args, **kwargs):
start_time = time.time()
result = fn(*args, **kwargs)
end_time = time.time()
print(f"Execution time for {fn.__name__}: {(end_time-start_time)*1000}ms")
return result
return wrapper
``````

Note that the wrapper function takes an arbitrary number of positional and keyword arguments using `*args` and `**kwargs`. This allows the decorator to be used on functions with any number of arguments.

To use the `test_time` decorator on the Euclidean algorithm function, we simply declare `@test_time` above the function definition, like so:

``````@test_time
def euclidean_algorithm(a,b):
while b!=0:
temp = b
b = a % b
a = temp
return a
``````

Now, when we run the function, the decorator will automatically measure the execution time and print the results to the console.

## Enhancing Functionality with Decorators in Python

In Python, we can enhance the functionality of our functions using decorators. A decorator is a special type of function that can modify or extend the functionality of another function without changing its source code.

### 1. Using Wrappers to Call Functions

One way to use decorators in Python is by using wrappers to call functions. A wrapper is a function that takes in another function and adds some sort of functionality to it.

For example, suppose we have a function called gardot that we want to add some extra functionality to. We can create a wrapper function that takes in gardot as an argument and then calls it, passing in additional information or modifying its behavior.

To demonstrate, suppose we have the following code:

``````def gardot():
print("Hello from gardot!")

def wrapper(func):
def inner():
print("Before the function is called.")
func()
print("After the function is called.")
return inner

gardot = wrapper(gardot)
``````

We have defined two functions, gardot and wrapper. The wrapper function takes in a function as an argument and then returns a new function that wraps the original function. In our case, we pass in gardot as an argument to wrapper and then assign the result back to gardot.

Now, when we call gardot, it will actually call the wrapper function, which in turn will call the original gardot function, but with additional functionality added. For example:

``````gardot()
``````

This will output:

``````Before the function is called.
Hello from gardot!
After the function is called.
``````

### 2. Adding Functionality with Decorators

Another way to use decorators in Python is by adding functionality to a function directly using the @ symbol. This is called function decoration.

For example, suppose we have a function called fn that we want to add some extra functionality to. We could create a decorator function that adds some sort of behavior to fn.

To demonstrate, suppose we have the following code:

``````def measure_time(func):
import time
def wrapper(*args, **kwargs):
start = time.time()
result = func(*args, **kwargs)
end = time.time()
print("Execution time: ", end - start, "seconds.")
return result
return wrapper

@measure_time
def fn(n):
for i in range(n):
print(i)
``````

We have defined a function called measuretime, which takes in a function as an argument and returns a new function that measures the execution time of the original function. We then decorate the fn function with the measuretime decorator by adding the @measure_time symbol before the function definition.

Now, when we call fn, it will actually call the wrapper function created by measure_time, which will in turn call the original fn function with the added functionality of measuring the execution time. For example:

``````fn(100000)
``````

This will output:

``````0
1
2
...
Execution time: 0.015625 seconds.
``````

By using decorators in Python, we can enhance the functionality of our functions in a flexible and modular way. Whether by using wrappers or function decoration, decorators offer a powerful way to modify or extend the behavior of our code.

## Understanding Closure in Decorators

In this article, we will dive into the concept of closure in decorators. As we know, decorators are used to modify or add functionality to existing functions without actually modifying their source code. Closures are an important aspect of decorators, and understanding them is crucial to mastering the art of writing decorators.

### The less flexible approach

Let's first take a look at a less flexible approach to writing decorators. The following code snippet demonstrates how to decorate a function called 'berkut' with a decorator function called 'wrap'.

``defwrap(fn):defwrapper(x):print("Before calling function...")result=fn(x)print("After calling function...")returnresultreturnwrapper@wrapdefberkut(n):returnn**2``

Here, the 'wrap' decorator takes a function and returns a new function called 'wrapper', which wraps the original function 'fn'. We then use the '@wrap' syntax to decorate the 'berkut' function with the 'wrap' decorator.

However, there's a downside to this approach. Whenever we want to call 'berkut' with an argument 'n', we need to explicitly pass 'berkut' as the first argument to 'wrapper' like so:

``berkut_result=berkut(5)# this worksberkut_result=wrapper(berkut,5)# this doesn't work``

This makes our code less flexible and harder to read and maintain.

### The more flexible approach

To make our code more flexible, we can create a new function with a different name that calls the original function and passes its arguments. The following code demonstrates this approach:

``defwrap(fn):defwrapper(*args,**kwargs):print("Before calling function...")result=fn(*args,**kwargs)print("After calling function...")returnresultreturnwrapper@wrapdeftest1(n):returnn**2``

Here, we've created a new function called 'test1', which calls the 'berkut' function with the passed arguments using the '' and '*' syntax to accept any number of arguments and keyword arguments.

Now, whenever we call the 'test1' function with an argument 'n', the 'wrapper' function is called automatically, wrapping the 'test1' function with the added functionality provided by the 'wrap' decorator.

### Closing thoughts

In summary, understanding closure in decorators is essential to writing flexible, maintainable, and readable code. By using closures, we can create a new function with a different name that calls the original function, making our code more flexible and avoiding the need to pass the original function as an argument to the decorator wrapper function.

## Enhancing the Performance of Functions in Python

In Python programming, it is important to optimize the performance of functions, especially when dealing with large amounts of data or complex algorithms. In this article, we will discuss various ways to enhance the performance of functions in Python.

### The Strict Euclidean Algorithm

One of the most commonly used algorithms in computer science is the Euclidean algorithm, which is used to find the greatest common divisor of two integers. In Python, the strict implementation of the Euclidean algorithm can be achieved using the following code:

``````def gcd(a, b):
if b == 0:
return a
else:
return gcd(b, a % b)
``````

### Using Time to Test Function Performance

To test the performance of the `gcd` function, we can use the `time` library to measure the time it takes for the function to execute. We can also create a wrapper function that can be used for testing the performance of any other function. Here's an example of using the wrapper function:

``````import time

def time_it(func, *args, **kwargs):
start_time = time.time()
result = func(*args, **kwargs)
end_time = time.time()
print(f"Execution time of {func.__name__}: {end_time - start_time} seconds")
return result

# Testing the performance of the gcd function
time_it(gcd, 60, 48) # Output: Execution time of gcd: 0.00010085105895996094 seconds

# Testing the performance of another function
def test_2(a, b):
return a ** b

time_it(test_2, 2, 1000000) # Output: Execution time of test_2: 0.00012993812561035156 seconds
``````

### Writing Universal Functions with Optional Named Parameters

To make the wrapper function more universal, we can add optional named parameters to the function that will be passed to the function being tested, if provided. This can be achieved by modifying the `time_it` function as follows:

``````def time_it(func, *args, **kwargs):
start_time = time.time()
if kwargs:
result = func(*args, **kwargs)
else:
result = func(*args)
end_time = time.time()
print(f"Execution time of {func.__name__}: {end_time - start_time} seconds")
return result
``````

### Using Decorators to Enhance Function Performance

Python also provides a syntax for using decorators to enhance the performance of functions. A decorator is a special type of function that can be used to modify the behavior of another function. Here's an example of using a decorator function to enhance the `test_2` function:

``````def timer_decorator(func):
def wrapper(*args, **kwargs):
start_time = time.time()
result = func(*args, **kwargs)
end_time = time.time()
print(f"Execution time of {func.__name__}: {end_time - start_time} seconds")
return result
return wrapper

@timer_decorator
def test_2(a, b):
return a ** b

# Testing the performance of the test_2 function with decorator
test_2(2, 1000000) # Output: Execution time of test_2: 0.00013494491577148438 seconds
``````

## What are Function Decorators and Closures in Python?

Python is a popular programming language among developers due to its simplicity and flexibility. One of the most appreciated features of Python is the ability to enhance the functionality of existing functions without changing their code. This feature is achieved through the use of function decorators and closures.

## Function Decorators

Function decorators are a way to modify or enhance the behavior of an existing function. This is achieved by wrapping the function inside another function that adds extra functionality to it. The syntax for defining a decorator function in Python is by using `@decorator_name` above the function that we want to decorate.

Example:

``````def calculate_time(func):
def wrapper(*args, **kwargs):
import time
start_time = time.time()
result = func(*args, **kwargs)
end_time = time.time()
print(f"Execution time: {end_time - start_time} seconds")
return result
return wrapper

@calculate_time
def get_square(n):
return n**2

print(get_square(5))
``````

Here, we have defined a decorator function called `calculate_time` that calculates the execution time for a function. We have used `@calculate_time` decorator before the `get_square` function to add the extra functionality. When we run the program, it calculates the execution time for `get_square(5)` and prints it on the console.

## Closures

Closures are functions that have access to variables from their outermost (enclosing) scope, even after the outer function has completed the execution. In Python, closures are created by declaring a nested function inside an outer function and returning the inner function.

Example:

``````def outer_func():
message = "Hello"

def inner_func():
print(message)

return inner_func

my_func = outer_func()
my_func()
``````

In this example, we have defined an outer function called `outer_func` that has a nested function `inner_func`. The `inner_func` has access to the `message` variable from the enclosing scope of `outer_func`. We have assigned the inner function to a variable `my_func` and called it. It prints the value of the `message` variable on the console.

By using function decorators and closures, we can extend the functionality of our code without modifying the original functions, making our code more organized, reusable, and cleaner.

Python decorators are a powerful tool for extending the functionality of functions in python. by defining a decorator function that takes another function as an argument, we can easily add new features to the existing function without modifying its code. in this article, we demonstrated how to create a test for the euclidean algorithm function using a decorator function. with this knowledge, you can now use python decorators to create your own custom functions and tests.
In conclusion, optimizing the performance of functions in python is crucial for improving the efficiency of code execution. by using techniques such as measuring the execution time using the `time` library, writing universal functions with optional named parameters, and using decorators to enhance the behavior of functions, we can significantly improve the performance of our python programs.

Python provides us with a simple yet powerful way to modify and extend the behavior of functions through the use of function decorators and closures. By understanding these concepts, we can write more elegant and efficient Python code.

• There are many built-in decorators in Python such as `@staticmethod`, `@classmethod`, and `@property`.
• We can also chain multiple decorators one after another to enhance the same function.
• We can pass arguments to decorators to customize their behavior.
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