Function call and execution flow in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens when a function is called in Python?

The program pauses at the call, jumps to the function's code, runs it, then returns to continue after the call.

intermediate

What is the 'call stack' in function execution?

It is a structure that keeps track of active functions. Each call adds a frame; returning removes it.

beginner

Why does a function return a value?

To send back a result to where it was called, so the program can use that result next.

beginner

What happens if a function does not have a return statement?

It returns None by default, meaning no specific value is sent back.

intermediate

How does Python handle nested function calls?

Python completes the innermost function first, then uses its result in the outer function call.

What does the program do immediately after a function call?

A Jumps to the function's code and starts executing it

B Skips the function and continues the next line

C Ends the program

D Waits for user input

When a function is called, the program jumps to that function's code to run it.

What is stored in the call stack during function execution?

A Only the return values

B All variables in the program

C Active function calls and their local data

D User inputs

The call stack keeps track of active functions and their local information.

If a function has no return statement, what does it return?

A The last variable

B 0

C An error

D None

Functions without a return statement return None by default.

In nested function calls, which function runs first?

A None run

B The innermost function

C Both run simultaneously

D The outermost function

Python runs the innermost function first to get its result.

What happens after a function finishes executing?

A The program returns to the point after the function call

B The program restarts

C The program stops

D The function runs again automatically

After finishing, the program continues from where the function was called.

Explain the flow of execution when a function is called in Python.

Think about what happens step-by-step from call to return.

Describe what the call stack is and why it is important during function calls.

Imagine a stack of plates where each plate is a function call.

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