Function call and execution flow in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested function calls

What is the output of this Python code?

Python

def f(x):
    return x * 2

def g(y):
    return f(y) + 3

print(g(4))

A 7

B 8

C 11

D 14

💡 Hint

Remember to follow the order of function calls and operations step by step.

Function g calls f with y=4, so f(4) returns 8. Then g adds 3, so 8 + 3 = 11.

❓ Predict Output

intermediate

Value of variable after function call

What is the value of variable 'result' after running this code?

Python

def add_one(n):
    return n + 1

result = add_one(5)

A 6

B 5

C None

D Error

💡 Hint

Check what the function returns and what is assigned to 'result'.

The function adds 1 to 5, so result becomes 6.

❓ Predict Output

advanced

Output with recursive function

What is the output of this recursive function call?

Python

def countdown(n):
    if n == 0:
        return 'Done'
    else:
        return str(n) + ' ' + countdown(n-1)

print(countdown(3))

A Error

B "3 2 1 Done"

C "Done 3 2 1"

D "3 2 1 0 Done"

💡 Hint

Trace the function calls from n=3 down to 0.

The function concatenates numbers down to 1 and then adds 'Done'.

❓ Predict Output

advanced

Output with function modifying a list

What is printed after this code runs?

Python

def append_number(lst):
    lst.append(4)

numbers = [1, 2, 3]
append_number(numbers)
print(numbers)

A [1, 2, 3, 4]

B [4]

C [1, 2, 3]

D Error

💡 Hint

Think about how lists are passed to functions in Python.

The list is modified inside the function, so the original list has 4 appended.

❓ Predict Output

expert

Output of function with default and keyword arguments

What is the output of this code?

Python

def greet(name, greeting='Hello'):
    return f"{greeting}, {name}!"

print(greet('Alice'))
print(greet('Bob', greeting='Hi'))

A "Hi, Alice!\nHi, Bob!"

B "Hi, Alice!\nHello, Bob!"

C "Hello, Alice!\nHello, Bob!"

D "Hello, Alice!\nHi, Bob!"

💡 Hint

Check which greeting is used for each call.

First call uses default 'Hello', second call uses keyword argument 'Hi'.

Practice

1. What happens when you call a function in Python?

easy

A. The program restarts from the beginning.

B. The program stops running completely.

C. The program jumps to the function's code and runs it.

D. The function code is ignored.

Solution

1. Step 1: Understand function call behavior

   When a function is called, the program temporarily moves to the function's code to execute it.

2. Step 2: Recognize program flow after function

   After the function finishes, the program returns to where it left off and continues running.

3. Final Answer:

   The program jumps to the function's code and runs it. -> Option C

4. Quick Check:

   Function call = program runs function code [OK]

Hint: Calling a function runs its code then returns [OK]

Common Mistakes:

• Thinking the program stops after a function call
• Believing the function code is skipped
• Assuming the program restarts after calling a function

2. Which of the following is the correct way to call a function named greet in Python?

easy

A. greet()

B. call greet()

C. function greet()

D. run greet()

Solution

1. Step 1: Recall Python function call syntax

   In Python, you call a function by writing its name followed by parentheses, like greet().

2. Step 2: Eliminate incorrect options

   The incorrect options use keywords or syntax not used in Python for calling functions.

3. Final Answer:

   greet() -> Option A

4. Quick Check:

   Function call syntax = name + () [OK]

Hint: Call functions by name followed by parentheses [OK]

Common Mistakes:

• Adding extra keywords like 'call' or 'run'
• Using 'function' keyword to call
• Forgetting parentheses after function name

3. What is the output of this code?

def add(x, y):
    return x + y

result = add(3, 4)
print(result)

medium

A. 34

B. 7

C. None

D. Error

Solution

1. Step 1: Understand the function behavior

   The function add takes two numbers and returns their sum.

2. Step 2: Calculate the function call result

   Calling add(3, 4) returns 3 + 4 = 7, which is stored in result.

3. Step 3: Print the result

   The print(result) statement outputs 7.

4. Final Answer:

   7 -> Option B

5. Quick Check:

   3 + 4 = 7 [OK]

Hint: Return value is printed, so output is sum 7 [OK]

Common Mistakes:

• Thinking the function prints instead of returns
• Concatenating numbers as strings (34)
• Expecting None because of missing print inside function

4. Find the error in this code:

def greet():
    print("Hello")

print(greet)

medium

A. It prints the function object, not the greeting.

B. SyntaxError due to missing parentheses in function definition.

C. NameError because greet is not defined.

D. IndentationError inside the function.

Solution

1. Step 1: Analyze the print statement

   The code prints greet without parentheses, so it prints the function object, not the result of calling it.

2. Step 2: Understand function call vs reference

   To run the function and print "Hello", it should be print(greet()) with parentheses.

3. Final Answer:

   It prints the function object, not the greeting. -> Option A

4. Quick Check:

   Missing () means function object printed [OK]

Hint: Use parentheses to call function, else prints object [OK]

Common Mistakes:

• Thinking missing parentheses cause syntax error
• Assuming function is not defined
• Confusing function call with function reference

5. Given this code, what will be printed?

def outer():
    def inner():
        return "Inside inner"
    result = inner()
    return result

print(outer())

hard

A. Error

B. inner

C. None

D. "Inside inner"

Solution

1. Step 1: Understand nested function calls

   The function outer defines an inner function inner and calls it, storing its return value.

2. Step 2: Trace the return values

   inner() returns the string "Inside inner", which outer() then returns.

3. Step 3: Print the final returned value

   The print(outer()) statement prints "Inside inner".

4. Final Answer:

   "Inside inner" -> Option D

5. Quick Check:

   Nested call returns inner's string [OK]

Hint: Nested function returns value used by outer function [OK]

Common Mistakes:

• Thinking inner function name prints instead of its return
• Expecting None because inner is nested
• Assuming error due to nested function