Python Recursion

Which statement about recursion in Python is TRUE?

• Every recursive function must have a base case to prevent infinite recursion
• Recursion always runs faster than iteration
• Python has no limit on recursion depth
• Recursive functions cannot return values

Answer explanation

A base case stops further recursive calls and prevents infinite recursion.

What will this code print?

• 3
• 6
• 9
• Error

Answer explanation

factorial(3) = 3*factorial(2) = 3*2*factorial(1) = 3*2*1 = 6.

What happens if a recursive function has no base case?

• It will run faster
• It will return None
• It will cause a RecursionError
• It will exit after one call

Answer explanation

Without a base case, recursion continues until Python’s recursion limit is exceeded.

Output?

• 10
• 6
• 1234
• Error

Answer explanation

1+2+3+4 = 10.

Which of the following is NOT a good use of recursion?

• Tree traversal
• Factorial calculation
• Processing very large loops without a base case
• Fibonacci number calculation

Answer explanation

Recursive calls without a base case will cause a RecursionError.

What is the output?

• 2
• 3
• 5
• 4

Answer explanation

fib(4) = fib(3) + fib(2) = 2 + 1 = 3.

In Python, the default recursion depth limit can be checked using:

• sys.getrecursionlimit()
• recursion.limit()
• get.limit()
• sys.limit()

Answer explanation

sys.getrecursionlimit() returns the current recursion depth limit.

What is tail recursion?

• A recursive call that appears at the start of a function
• A recursive call that appears at the end of a function with no further computation
• Recursion that uses a tail data structure
• Recursion that calls multiple functions

Answer explanation

Tail recursion has the recursive call as the last statement; Python does not optimize it.

What is printed?

• 9
• 12
• 6
• 15

Answer explanation

mystery(5) = 5 + mystery(3) = 5 + (3 + mystery(1)) = 5+3+1=9.

Which scenario is most suitable for recursion?

• Finding factorial of a small number
• Iterating over a list with millions of elements
• Computing the sum of two numbers
• Printing 'Hello' 5 times

Answer explanation

Recursion is ideal for problems with smaller inputs and clear sub-problems, like factorial.