Python Coding challenge - Day 1273| What is the output of the following Python Code?

 

Code Explanation:

1. 🏗️ Creating the Dictionary Subclass

class D(dict):

Here, D is a custom class that inherits from dict.

Therefore, objects of D behave like dictionaries, but we can also add custom behavior.

2. 🔍 Defining __missing__()

def __missing__(self, key):

__missing__() is a special dictionary method.

Python calls it when:

d[key]

is used and the key does not exist.

It is important that __missing__() is triggered by dictionary indexing, not by every dictionary lookup method.

3. 📏 Returning the Key Length

return len(key)

The missing key will be "python".

Therefore:

len("python") = 6

So __missing__() returns:

6

4. 🗂️ Creating the Dictionary

d = D()

An empty object of class D is created.

Initially:

d = {}

There is no "python" key.

5. 🎯 Accessing the Missing Key

x = d["python"]

Python looks for "python" inside d.

It doesn't find it.

Because D defines __missing__(), Python calls:

__missing__("python")

Then:

len("python")

returns:

6

Therefore:

x = 6

6. ⚠️ The Important .get() Difference

y = d.get("python")

This is the tricky line.

Even though "python" is missing, .get() does not call __missing__().

Since there is no "python" key, .get() returns:

None

Therefore:

y = None

7. 🖨️ Print the Result

print(x, y)

We have:

x = 6

y = None

So the output is:

6 None

Book: 400 Days Python Coding Challenges with Explanation