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Jan 2026 - Python - Week 9 - WEEK9-GrPA 5

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Jan 2026 - Python - Week 9 - WEEK9-GrPA 5

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Graded Assignment

Course: Jan 2026 - Python

WEEK9-GrPA 5

Submission deadline has passed for this assignment

Due Apr 17, 2026 at 11:59 PM IST

Instructions

Use "Test Run" to verify your code with public test cases.

Press "Submit" to have your assignment evaluated.

You can submit your assignment multiple times up until the deadline.

Make sure to submit your final code by the deadline to receive your score.

Summary

100 out of100

Score

Public Tests

2/2 Passed

Submitted on Apr 17, 2026 at 5:35 AM IST

Private Tests

5/5 Passed

Submitted on Apr 17, 2026 at 5:35 AM IST

P is a dictionary of father-son relationships that has the following structure: for any key in the dictionary, its corresponding value is the father of key. As an example:


P = {
    'Jahangir': 'Akbar',
    'Akbar': 'Humayun',
    'Humayun': 'Babur'
}

If 'Jahangir' is the key, then 'Akbar', his father, is the value. This is true of every key in the dictionary.

Write a recursive function named ancestry that accepts the following arguments:

P: dictionary of relationships
present: name of a person, string
past: name of a person, string

It should return the sequence of ancestors of the person named present, traced all the way back up to person named past. For example, ancestry(P, 'Jahangir', 'Babur') should return the list:


L = ['Jahangir', 'Akbar', 'Humayun', 'Babur']

In more Pythonic terms, L[i] is the father of L[i - 1], for

1 \leq i < \text{len}(L)

, with the condition that L[0] should be present and L[-1] should be past.

(1) You can assume that no two persons in the dictionary have the same name. However, a given person could either appear as a key or as a value in the dictionary.

(2) A given person could appear multiple times as one of the values of the dictionary. For example, in test-case-2, Prasanna has two sons, Mohan and Krishna, and hence appears twice (as a value).

(3) You do not have to accept input from the user or print output to the console. You just have to write the function definition.

Public Tests ( 2/2 )

Case 1

Input:


text
public
{'Jahangir': 'Akbar', 'Akbar': 'Humayun', 'Humayun': 'Babur'}
Jahangir
Babur

Expected Output:


text
['Jahangir', 'Akbar', 'Humayun', 'Babur']

Actual Output:


text
['Jahangir', 'Akbar', 'Humayun', 'Babur']

Case 2

Input:


text
public
{'Anil': 'Krishna', 'Mohan': 'Prasanna', 'Krishna': 'Prasanna', 'Prasanna': 'Mukesh'}
Anil
Prasanna

Expected Output:


text
['Anil', 'Krishna', 'Prasanna']

Actual Output:


text
['Anil', 'Krishna', 'Prasanna']

Private Tests ( 5/5 )

Case 1

Input:


text
private
{'Sam': 'Peter', 'George': 'Peter', 'Peter': 'John', 'John': 'Alex', 'Alex': 'Andrew', 'Andrew': 'Adam'}
George
Andrew

Expected Output:


text
['George', 'Peter', 'John', 'Alex', 'Andrew']

Good, your function is recursive

Actual Output:


text
['George', 'Peter', 'John', 'Alex', 'Andrew']

Good, your function is recursive

Case 2

Input:


text
private
{'Sam': 'Peter', 'George': 'Peter', 'Peter': 'John', 'John': 'Alex', 'Alex': 'Andrew', 'Andrew': 'Adam'}
Sam
Adam

Expected Output:


text
['Sam', 'Peter', 'John', 'Alex', 'Andrew', 'Adam']

Good, your function is recursive

Actual Output:


text
['Sam', 'Peter', 'John', 'Alex', 'Andrew', 'Adam']

Good, your function is recursive

Case 3

Input:


text
private
{'Jahangir': 'Akbar', 'Akbar': 'Humayun', 'Humayun': 'Babur'}
Humayun
Babur

Expected Output:


text
['Humayun', 'Babur']

Good, your function is recursive

Actual Output:


text
['Humayun', 'Babur']

Good, your function is recursive

Case 4

Input:


text
private
{'Anil': 'Krishna', 'Mohan': 'Prasanna', 'Krishna': 'Prasanna','Sachin': 'Prasanna', 'Prasanna': 'Sourav'}
Mohan
Sourav

Expected Output:


text
['Mohan', 'Prasanna', 'Sourav']

Good, your function is recursive

Actual Output:


text
['Mohan', 'Prasanna', 'Sourav']

Good, your function is recursive

Case 5

Input:


text
private
{'Anil': 'Krishna', 'Mohan': 'Prasanna', 'Krishna': 'Prasanna','Sachin': 'Prasanna', 'Prasanna': 'Sourav'}
Anil
Sourav

Expected Output:


text
['Anil', 'Krishna', 'Prasanna', 'Sourav']

Good, your function is recursive

Actual Output:


text
['Anil', 'Krishna', 'Prasanna', 'Sourav']

Good, your function is recursive

💻 IITM Official Solution


python
def ancestry(P, present, past):
    if present == past:
        return [past]
    return [present] + ancestry(P, P[present], past)

💻 My Submitted Code


python
def ancestry(P, present, past):
    """
    A recursive function to compute the sequence of ancestors of person

    Arguments:
        P: dict, key and value are strings
        present: string
        past: string
    Return:
        result: list of strings
    """
    # Base case
    if present == past:
        return [present]

    # Recursive case
    return [present] + ancestry(P, P[present], past)