Q.Assuming that D1 is a dictionary in Python,

Concept: Dictionary membership testing, the get() method with default insertion via setdefault(), and dictionary clearing.

(i) (a) Check if key 'RNo' is present

Use the in operator on the dictionary's keys:

'RNo' in D1

This returns True if the key exists, False otherwise.

(i) (b) Check if any key has value 12

Use the in operator on the dictionary's values:

12 in D1.values()

This returns True if at least one key maps to 12.

(ii) (a) Add key-value pair if absent, else return existing value

The setdefault() method does exactly this in one statement:

D1.setdefault('RNo', 12)

If 'RNo' is missing, it inserts 'RNo': 12 and returns 12. If 'RNo' already exists, it returns the current value without modification. …

Python dictionaries are hash tables that map keys to values. The language provides elegant, built-in ways to test membership, conditionally insert, and manipulate these mappings without verbose if-else blocks.

Part (i): Membership Testing

(a) Check if key 'RNo' is present

The in operator tests membership in a dictionary's key space by default. It returns a boolean and runs in average constant (O(1)) time thanks to hashing.

'RNo' in D1

This expression evaluates to True if 'RNo' is a key in D1, False otherwise.

(b) Check if any key has value 12

Values are not hashed, so we must search through them. The .values() method returns a view of all values; combine it with in:

12 in D1.values()

This scans the values linearly (worst-case O(n)) and returns True if at least one key maps to 12.

Part (ii): Conditional Insertion and Deletion

(a) Add 'RNo': 12 if absent, else return existing value

Python's setdefault(key, default) method is purpose-built for this: it returns D1[key] if the key exists, otherwise inserts key with value default and returns default.

D1.setdefault('RNo', 12)

How it works:

1. Checks if 'RNo' is in D1.
2. If present, returns the current value (no modification).
3. If absent, sets D1['RNo'] = 12 and returns 12.

This is cleaner than the equivalent: