Python Coding challenge - Day 731| What is the output of the following Python Code?

 

Code Explanation:

1. Importing defaultdict

from collections import defaultdict

Imports defaultdict from Python’s collections module.

A defaultdict is like a normal dictionary, but it automatically creates a default value for missing keys, based on the factory function you pass.

2. Creating a defaultdict of lists

d = defaultdict(list)

Creates a dictionary d where each missing key will automatically be assigned an empty list [].

So, if you do d["x"] and "x" doesn’t exist, it will create d["x"] = [].

3. List of key-value pairs

pairs = [("a", 1), ("b", 2), ("a", 3)]

Defines a list of tuples.

Each tuple has a key and a value.

Data:

"a" → 1

"b" → 2

"a" → 3

4. Loop to fill defaultdict

for k, v in pairs:

    d[k].append(v)

Iterates over each (key, value) in pairs.

For key "a":

d["a"] doesn’t exist → defaultdict creates [].

Then .append(1) → now d["a"] = [1].

For key "b":

d["b"] doesn’t exist → defaultdict creates [].

Then .append(2) → now d["b"] = [2].

For key "a" again:

d["a"] already exists [1].

.append(3) → now d["a"] = [1, 3].

After loop → d = {"a": [1, 3], "b": [2]}

5. Printing results

print(len(d), d["a"], d.get("c"))

len(d) → number of keys = 2 ("a" and "b").

d["a"] → [1, 3].

d.get("c") → Since "c" doesn’t exist, .get() returns None (no error).

Final Output

2 [1, 3] None

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