Python Coding challenge - Day 470| What is the output of the following Python Code?

 

Code Explanation:

 Function Definition with a Mutable Default Argument

def f(key, val, d={}):

    d[key] = val

    return d

A function f is defined with three parameters: key, val, and d (defaulting to an empty dictionary {}).

Important: In Python, default values are evaluated only once, at the time the function is defined, not each time it's called.

So d={} creates one shared dictionary used across calls that don't provide a new one.

First Call: f('a', 1)

f('a', 1)

key='a', val=1, d uses the default value {}.

Adds 'a': 1 to d, so now:

d = {'a': 1}

Second Call: f('b', 2)

f('b', 2)

key='b', val=2, again uses the same default dictionary d.

Adds 'b': 2, so now:

d = {'a': 1, 'b': 2}

Third Call and Final Output

print(f('c', 3)['a'])

key='c', val=3, again uses the same shared dictionary.

Adds 'c': 3, so now:

d = {'a': 1, 'b': 2, 'c': 3}

Then f('c', 3)['a'] retrieves the value of key 'a' → 1

 Final Output

1