Method invocation flow in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is method invocation flow in Python?

It is the order in which Python runs the code inside a method when you call it on an object. The program jumps to the method, runs its steps, then returns to where it was called.

beginner

What happens when you call a method on an object?

Python looks for the method in the object's class, runs the code inside that method, and then goes back to continue the rest of the program.

beginner

How does Python handle self in method calls?

self is the object itself. When you call a method, Python passes the object as the first argument automatically, so you can use self to access its data.

intermediate

What is the flow when a method calls another method inside it?

Python pauses the first method, runs the second method fully, then returns to finish the first method.

beginner

Why is understanding method invocation flow important?

It helps you know how your program runs step-by-step, making it easier to find mistakes and write clear code.

When you call a method on an object, what does Python do first?

A Deletes the object

B Runs the whole program again

C Looks for the method in the object's class

D Skips the method

Python first finds the method inside the object's class before running it.

What does self represent inside a method?

A The method itself

B The Python interpreter

C A global variable

D The object calling the method

self is the object that called the method, letting you access its data.

If a method calls another method, what happens to the first method?

A It pauses until the second method finishes

B It stops running forever

C It runs both methods at the same time

D It deletes the second method

The first method waits (pauses) until the second method finishes before continuing.

What is the last step in method invocation flow?

A Start the program over

B Return to the place where the method was called

C Delete the method

D Ignore the method's result

After running the method, Python returns to the spot where the method was called to continue.

Why should you understand method invocation flow?

A To know how your program runs step-by-step

B To make your computer run cooler

C To write code that runs faster

D To avoid using methods

Understanding the flow helps you follow your program's steps and fix errors easily.

Explain the steps Python takes when you call a method on an object.

Think about what happens from the moment you write object.method()

Describe what happens when one method calls another method inside it.

Imagine a friend asking another friend for help before finishing their own task.

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