Method invocation flow in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the method greet on the object person.

Python

class Person:
    def greet(self):
        print("Hello!")

person = Person()
person.[1]()

Drag options to blanks, or click blank then click option'

Asay_hello

Bhello

Cgreet

Dgreeting

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong method name that does not exist.

Forgetting the parentheses to call the method.

The method defined is named greet, so calling person.greet() runs it.

2fill in blank

medium

Complete the code to call the method add with argument 5 on the object calc.

Python

class Calculator:
    def add(self, x):
        return x + 10

calc = Calculator()
result = calc.[1](5)
print(result)

Drag options to blanks, or click blank then click option'

Asum

Bcalculate

Cplus

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not exist.

Forgetting to pass the argument inside parentheses.

The method to add is named add, so calling calc.add(5) returns 15.

3fill in blank

hard

Fix the error by completing the code to call the method display on the object obj.

Python

class Display:
    def display(self):
        print("Showing content")

obj = Display()
obj[1]

Drag options to blanks, or click blank then click option'

A.display

B.display()

Cdisplay()

D->display()

Attempts:

3 left

💡 Hint

Common Mistakes

Missing the dot before the method name.

Missing the parentheses to call the method.

To call a method, you need the dot and parentheses: obj.display().

4fill in blank

hard

Fill both blanks to complete the method call that returns the length of the string stored in obj.text.

Python

class TextHolder:
    def __init__(self, text):
        self.text = text

obj = TextHolder("hello")
length = len(obj.text[1]()) if obj.text [2] "" else 0
print(length)

Drag options to blanks, or click blank then click option'

Astrip

B!=

C==

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators.

Using a method that does not exist on strings.

We call strip() to remove spaces, and check if obj.text != "" to ensure it's not empty.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each word to its uppercase form if the word length is greater than 3.

Python

words = ["apple", "cat", "banana", "dog"]
result = { [1]: [2] for [3] in words if len(word) > 3 }
print(result)

Drag options to blanks, or click blank then click option'

Aword

Bword.upper()

D{word}

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces around the key incorrectly.

Mixing up the key and value positions.

Using wrong variable names.

The dictionary comprehension uses {word: word.upper() for word in words if len(word) > 3} to map words longer than 3 letters to uppercase.

Practice

1. What does method invocation flow describe in Python?

easy

A. The order in which methods are called and executed

B. The way variables are declared inside methods

C. How to write comments inside methods

D. The syntax rules for defining methods

Solution

1. Step 1: Understand the term 'method invocation'

   Method invocation means calling a method to run its code.

2. Step 2: Understand 'flow' in this context

   Flow means the order or sequence in which these method calls happen.

3. Final Answer:

   The order in which methods are called and executed -> Option A

4. Quick Check:

   Method invocation flow = method call order [OK]

Hint: Think: When you call methods, what order do they run? [OK]

Common Mistakes:

• Confusing method flow with variable declaration
• Thinking it means method syntax rules
• Mixing it up with comments inside methods

2. Which of the following is the correct way to call a method named greet on an object person?

easy

A. greet.person()

B. person.greet()

C. person->greet()

D. greet(person)

Solution

1. Step 1: Recall Python method call syntax

   In Python, to call a method on an object, use dot notation: object.method()

2. Step 2: Check each option

   person.greet() uses correct dot notation with parentheses. Others use invalid syntax or function call style.

3. Final Answer:

   person.greet() -> Option B

4. Quick Check:

   Object.method() is correct call syntax [OK]

Hint: Remember: object.method() calls a method in Python [OK]

Common Mistakes:

• Using arrow (->) like other languages
• Reversing object and method order
• Calling method without parentheses

3. What is the output of this code?

class A:
    def first(self):
        print('First')
        self.second()
    def second(self):
        print('Second')

obj = A()
obj.first()

medium

A. Second

B. Second\nFirst

C. First\nSecond

D. First

Solution

1. Step 1: Trace method calls

   Calling obj.first() prints 'First' then calls self.second(), which prints 'Second'.

2. Step 2: Determine output order

   Output is 'First' then 'Second' on separate lines.

3. Final Answer:

   First\nSecond -> Option C

4. Quick Check:

   Method calls run in order called [OK]

Hint: Follow method calls step-by-step to find output order [OK]

Common Mistakes:

• Assuming second() runs before first()
• Missing the call to second() inside first()
• Thinking only first print runs

4. Find the error in this code:

class B:
    def start(self):
        self.middle()
    def middle(self):
        self.end()
    def end(self):
        print('Done')

b = B()
b.middle()

medium

A. No output because start() is not called

B. AttributeError because end() is not defined

C. TypeError due to missing arguments

D. No error, prints 'Done'

Solution

1. Step 1: Check method definitions

   All methods are defined correctly with self parameter.

2. Step 2: Check method call

   b.middle() calls self.end(), which prints 'Done'. So output is 'Done' with no error.

3. Final Answer:

   No error, prints 'Done' -> Option D

4. Quick Check:

   Calling middle() runs end() correctly [OK]

Hint: Trace calls from the method you invoke to see output [OK]

Common Mistakes:

• Expecting start() must be called first
• Thinking end() is undefined
• Confusing missing arguments error

5. Given this code, what will be printed?

class C:
    def a(self):
        print('A')
        self.b()
    def b(self):
        print('B')
        self.c()
    def c(self):
        print('C')

c = C()
c.a()

hard

A. A\nB\nC

B. A\nC\nB

C. C\nB\nA

D. B\nC\nA

Solution

1. Step 1: Follow method calls starting from c.a()

   c.a() prints 'A' then calls self.b()

2. Step 2: Trace self.b() and self.c()

   self.b() prints 'B' then calls self.c(), which prints 'C'.

3. Step 3: Combine outputs in order

   Output is 'A' then 'B' then 'C' each on new lines.

4. Final Answer:

   A\nB\nC -> Option A

5. Quick Check:

   Method calls chain in order a->b->c [OK]

Hint: Follow each method call in order to find print sequence [OK]

Common Mistakes:

• Mixing order of method calls
• Skipping intermediate method calls
• Assuming methods run independently