Self reference in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a self-referencing dictionary

What is the output of this Python code that uses a dictionary referencing itself?

Python

d = {}
d['self'] = d
print(d['self'] is d)

A KeyError

B False

C TypeError

D True

💡 Hint

Think about whether the dictionary stored inside the key 'self' is the same object as d.

The dictionary d stores itself under the key 'self'. So d['self'] points to the same dictionary object as d, making the identity check True.

❓ Predict Output

intermediate

Output of a self-referencing list

What will this Python code print?

Python

lst = [1, 2]
lst.append(lst)
print(len(lst))

A 3

B 2

C TypeError

D RecursionError

💡 Hint

Appending the list to itself adds one more element.

The list initially has 2 elements. Appending itself adds a third element which is the list itself, so length becomes 3.

🔧 Debug

advanced

Why does this self-referencing class cause infinite recursion?

Consider this Python class that references itself in a method. What causes the infinite recursion error?

Python

class Node:
    def __init__(self):
        self.child = self
    def get_child(self):
        return self.child.get_child()

n = Node()
n.get_child()

A The class Node is not instantiated properly

B self.child is None causing AttributeError

C get_child calls itself endlessly because self.child is self

D The constructor __init__ is missing a return statement

💡 Hint

Look at what get_child returns and what self.child points to.

The method get_child calls itself recursively because self.child is the same Node instance, so get_child calls get_child endlessly causing infinite recursion.

🧠 Conceptual

advanced

Understanding self-reference in nested data structures

What is the output of this code that creates a nested dictionary referencing itself?

Python

a = {}
a['nested'] = {'parent': a}
print(a['nested']['parent'] is a)

A False

B True

C KeyError

D TypeError

💡 Hint

Check if the nested dictionary's 'parent' key points back to the original dictionary.

The nested dictionary inside 'nested' has a key 'parent' that points back to the original dictionary a, so the identity check is True.

❓ Predict Output

expert

Output of printing a self-referencing list

What is the output of this Python code?

Python

lst = [1, 2]
lst.append(lst)
print(lst)

A [1, 2, [...]]

B [1, 2, [1, 2]]

C RecursionError

D [1, 2, None]

💡 Hint

Python shows self-references in lists with [...].

When printing a list that contains itself, Python shows the self-reference as [...], so the output is [1, 2, [...]].