Method invocation flow in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained method calls

What is the output of this Python code involving chained method calls?

Python

class TextProcessor:
    def __init__(self, text):
        self.text = text
    def to_upper(self):
        self.text = self.text.upper()
        return self
    def add_exclamation(self):
        self.text += '!'
        return self
    def get_text(self):
        return self.text

result = TextProcessor('hello').to_upper().add_exclamation().get_text()
print(result)

A "hello"

B "hello!"

C "HELLO"

D "HELLO!"

💡 Hint

Look at how each method modifies the text and returns self for chaining.

The methods to_upper and add_exclamation both modify the text and return the object itself, allowing chaining. Finally, get_text returns the modified string 'HELLO!'.

❓ Predict Output

intermediate

Method call order and output

What will be printed when this code runs?

Python

class Counter:
    def __init__(self):
        self.count = 0
    def increment(self):
        self.count += 1
        return self
    def double(self):
        self.count *= 2
        return self
    def get(self):
        return self.count

c = Counter()
print(c.increment().double().increment().get())

A 4

B 3

C 2

D 5

💡 Hint

Trace the count value step by step through each method call.

Starting at 0: increment() makes 1, double() makes 2, increment() makes 3, get() returns 3.

🔧 Debug

advanced

Identify the error in method chaining

This code tries to chain methods but raises an error. What is the error type?

Python

class Builder:
    def __init__(self):
        self.value = ''
    def add_a(self):
        self.value += 'a'
    def add_b(self):
        self.value += 'b'
    def get_value(self):
        return self.value

b = Builder()
print(b.add_a().add_b().get_value())

A NoneType has no attribute 'add_b'

B TypeError

C SyntaxError

D AttributeError

💡 Hint

Check what each method returns and how chaining works.

Methods add_a and add_b do not return self, so add_a() returns None. Then None.add_b() causes an AttributeError: 'NoneType' object has no attribute 'add_b'.

🧠 Conceptual

advanced

Understanding method invocation flow with inheritance

Given these classes, what will be the output of the code below?

Python

class Base:
    def action(self):
        return 'Base'
class Child(Base):
    def action(self):
        return 'Child' + super().action()

obj = Child()
print(obj.action())

A "ChildBase"

B "BaseChild"

C "Child"

D "Base"

💡 Hint

Look at how super() calls the parent method inside the child method.

Child's action method returns 'Child' plus the result of Base's action method, which is 'Base', so the output is 'ChildBase'.

❓ Predict Output

expert

Complex method invocation with side effects

What is the final output of this code?

Python

class Tracker:
    def __init__(self):
        self.log = []
    def step1(self):
        self.log.append('1')
        return self
    def step2(self):
        self.log.append('2')
        return self
    def step3(self):
        self.log.append('3')
        return self
    def get_log(self):
        return ''.join(self.log)

tracker = Tracker()
result = tracker.step1().step2().step1().step3().get_log()
print(result)

A "123"

B "1123"

C "1213"

D "213"

💡 Hint

Follow the order of method calls and what each appends to the log.

The calls append '1', then '2', then '1' again, then '3', so the log is '1213'.