Impara Python Decorator Syntax: Writing and Applying Decorators

Decorator works by taking a function as an argument and then executing it within a wrapper function.

To apply a decorator, one can use the @ symbol followed by the decorator function's name, placed right above the function that needs to be modified. Here's an example:

def decorator(func):
    ...

# First method
@decorator
add(a,b):
    print(f"Function add: {a} + {b}")

add(2, 3)

# Second method
add(a,b):
    print(f"Function add: {a} + {b}")

inner = decorator(add)

inner(2, 3)

In this example, both methods achieve the same outcome. The first method, using the @ symbol, is a more readable and concise way to apply decorators, often referred to as "syntactic sugar".

It's typical to use a nested function named wrapper within decorators.

Flexible Decorators: Accommodating Diverse Function Arguments

Functions often require a varying number of arguments. To develop a decorator capable of being applied to functions with differing argument counts, it's effective to utilize *args and **kwargs in the wrapper() function.


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def indicate(func):
    def wrapper(*args, **kwargs):
        print("=" * 15)
        print("Taken arguments:", *args, kwargs)
        result = func(*args, **kwargs)
        print("=" * 15)
        return result
    return wrapper


@indicate
def avg_two(a, b):
    """Calculate the average of two numbers"""
    return round((a + b) / 2, 1)

@indicate
def avg_three(a, b, c):
    """Calculate the average of three numbers"""
    return round((a + b + c) / 3, 1)

@indicate
def avg_many_kwargs(**kwargs):
    """Calculate the average of multiple numbers in a dictionary"""
    keys = 0
    total = 0

    for value in kwargs.values():
        keys += 1
        total += value

    return round(total / keys, 1)

print("Returned:", avg_two(14, 21), "\n")
print("Returned:", avg_three(225, 12, 11), "\n")
print("Returned:", avg_many_kwargs(first=51, second=11, third=47, fourth=93))

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Sezione 5. Capitolo 2

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