Python Coding challenge - Day 1286| What is the output of the following Python Code?

 

Code Explanation:

1. def outer(x): — Outer Function

def outer(x):

- Defines a function named outer().

- It accepts one parameter, x.

- When we call outer(2), the variable x starts with the value 2.

- The variable x belongs to the local scope of outer().

2. def inner(y): — Nested Function

def inner(y):

- Defines a function named inner() inside outer().

- This is called a nested function.

- It accepts one parameter, y.

- The inner function can access variables from its enclosing function.

3. nonlocal x — Modify the Enclosing Variable

nonlocal x

- The nonlocal keyword refers to the variable x from the enclosing function.

- It allows inner() to modify the existing x instead of creating a new local variable.

- The value of x will persist between calls to inner().

4. x += y — Update the Value

x += y

- Adds y to the current value of x.

- Updates the enclosing variable x.

For the first call:

f(3)

Calculation:

x = 2 + 3

x = 5

For the second call:

f(4)

Calculation:

x = 5 + 4

x = 9

5. return lambda z: x * z — Return a Lambda Function

return lambda z: x * z

- lambda creates an anonymous function.

- It accepts one parameter, z.

- It returns the product of x and z.

- The returned lambda remembers the enclosing variable x. This behavior is related to a closure.

After the first call, a stores a lambda function. After the second call, b stores another lambda function. Both reference the same enclosing variable x.

6. return inner — Return the Inner Function

return inner

- Returns the function inner itself, rather than calling it.

- This allows us to store that function in another variable.

- The enclosing scope remains available even after outer() has finished executing.

7. f = outer(2) — Create the Function

f = outer(2)

- Calls outer() with x = 2.

- The function returns inner.

- The variable f now refers to the inner function.

8. a = f(3) — First Function Call

a = f(3)

- Calls inner(y) with y = 3.

- Updates x from 2 to 5.

- Returns a lambda function, which is stored in a.

At this point, a refers to a lambda that uses the shared variable x.

9. b = f(4) — Second Function Call

b = f(4)

- Calls inner(y) with y = 4.

- The current value of x is 5.

- Updates x to 9.

- Returns another lambda function, which is stored in b.

Important: Both a and b refer to lambdas that access the same variable x. Its current value is now 9.

10. print(a(2), b(2)) — Final Output

print(a(2), b(2))

- a(2) calculates 9 * 2 = 18.

- b(2) also calculates 9 * 2 = 18.

- Both lambdas use the latest value of the shared variable x.

Output:

18 18

Books: 400 Days Python Coding Challenges with Explanation