Python Coding challenge - Day 590| What is the output of the following Python Code?

 

Code Explanation:

Function Definition – decorate(f)

def decorate(f):

What it does:

Defines a higher-order function named decorate.

It takes a function f as a parameter.

This will be used to wrap another function (via a decorator).

Inner Function – wrap(x)

    def wrap(x): return [f(x)]

What it does:

Defines an inner function called wrap.

wrap(x) calls the original function f(x) and wraps the result in a list.

Example: if f(x) returns 8, then wrap(x) returns [8].

Return the Wrapper Function

    return wrap

What it does:

Returns the wrap function.

So now, decorate(f) doesn't return a value — it returns a new function that wraps f.

Use of Decorator – @decorate

@decorate

def double(x): return x * 2

What it does:

@decorate is a decorator syntax.

It is equivalent to:

def double(x): return x * 2

double = decorate(double)

This means the original double(x) (which returns x * 2) is replaced with the wrapped version: a function that returns [x * 2].

Function Call and Output

print(double(4)[0])

What it does:

double(4) now calls the wrapped version, not the original.

So:

double(4) → [4 * 2] → [8]

[0] accesses the first element of the list:

[8][0] → 8

print(8) prints 8 to the console.

Final Output:

8

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