Python Coding challenge - Day 814| What is the output of the following Python Code?

 Code Explanation:

from collections import defaultdict

What this does:

Imports defaultdict from Python’s collections module.

defaultdict behaves like a regular dict but if you access a missing key it will automatically create it with a default value provided by a factory function (here int).

d = defaultdict(int)

What this does:

Creates a defaultdict named d whose default factory is int.

int() returns 0, so any new key accessed in d will start with value 0 instead of raising KeyError.

Equivalent behavior if you later do d[99] (when key 99 doesn't exist): d[99] becomes 0.

for i in [1,2,1,3]:

What this does:

Starts a for loop that will iterate over the list [1, 2, 1, 3].

Each iteration, the loop variable i takes one element from the list in order: 1, then 2, then 1, then 3.

d[i] += 1

What this does (inside the loop):

On each iteration it increments the counter stored at key i in the defaultdict.

If the key i does not yet exist, defaultdict(int) creates it with initial value 0, then += 1 increases it to 1.

Step-by-step state changes:

Iteration 1 (i=1): d[1] was created as 0 → becomes 1. ⇒ d = {1:1}

Iteration 2 (i=2): d[2] created 0 → becomes 1. ⇒ d = {1:1, 2:1}

Iteration 3 (i=1): d[1] exists (1) → becomes 2. ⇒ d = {1:2, 2:1}

Iteration 4 (i=3): d[3] created 0 → becomes 1. ⇒ d = {1:2, 2:1, 3:1}

print(d[1], d[2], d[3])

What this does:

Retrieves the values for keys 1, 2, and 3 from the defaultdict and prints them separated by spaces.

Based on the final state above, this prints:

2 1 1

Output:

2 1 1

600 Days Python Coding Challenges with Explanation