Comparison magic methods in Python - Step-by-Step Execution

Concept Flow - Comparison magic methods

Create object A

↓

Create object B

↓

Call __eq__?

Yes→Compare A and B for equality

↓

Return True/False

↓

Call __lt__?

Yes→Compare A < B

↓

Return True/False

↓

Call other comparison methods similarly

↓

Use result in if/print/etc

↓

End

Objects are created, then Python calls special methods like __eq__ or __lt__ to compare them, returning True or False.

Execution Sample

Python

class Box:
    def __init__(self, size):
        self.size = size
    def __eq__(self, other):
        return self.size == other.size

b1 = Box(5)
b2 = Box(5)
print(b1 == b2)

This code creates two Box objects and compares them using the __eq__ method to check if their sizes are equal.

Execution Table

Step	Action	Evaluation	Result
1	Create b1 with size=5	b1.size = 5	b1 object created
2	Create b2 with size=5	b2.size = 5	b2 object created
3	Compare b1 == b2	Call b1.__eq__(b2)	Return b1.size == b2.size
4	Evaluate b1.size == b2.size	5 == 5	True
5	Print result	print(True)	Output: True

💡 Comparison done, result True printed, program ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
b1.size	N/A	5	5	5	5
b2.size	N/A	N/A	5	5	5
comparison_result	N/A	N/A	N/A	True	True

Key Moments - 3 Insights

Why does b1 == b2 return True even though they are different objects?

Because the __eq__ method compares their sizes, not their memory addresses. See execution_table step 3 and 4 where __eq__ returns True based on size.

What happens if __eq__ is not defined?

Python would check if b1 and b2 are the exact same object (memory address), so b1 == b2 would be False. This is why defining __eq__ changes comparison behavior.

Can other comparison operators like < or > be customized similarly?

Yes, by defining __lt__, __gt__, __le__, __ge__ methods. Python calls these when using <, >, <=, >= respectively.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of b1 == b2 at step 4?

A True

B False

C Error

D None

💡 Hint

Check the 'Result' column at step 4 in execution_table.

At which step is the __eq__ method called?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column to find when __eq__ is invoked.

If b2.size was 6 instead of 5, what would be the output at step 5?

A True

B Error

C False

D None

💡 Hint

Compare sizes in execution_table step 4; different sizes mean __eq__ returns False.

Concept Snapshot

Comparison magic methods:
- __eq__(self, other): equality (==)
- __lt__(self, other): less than (<)
- __gt__(self, other): greater than (>)
- __le__, __ge__, __ne__ for other comparisons
Define these in classes to customize how objects compare.
Python calls these automatically during comparisons.

Full Transcript

This visual trace shows how Python uses comparison magic methods like __eq__ to compare objects. First, two Box objects are created with size 5. When comparing b1 == b2, Python calls b1.__eq__(b2), which compares their sizes. Since both sizes are 5, __eq__ returns True. This result is printed. If __eq__ was not defined, Python would compare object identities instead. Other comparison methods like __lt__ can be defined similarly to customize <, >, <=, >= behavior.