Python gt Method

Last modified April 8, 2025

This comprehensive guide explores Python’s gt method, the special method that implements the greater-than operator. We’ll cover basic usage, comparison operations, operator overloading, and practical examples.

Basic Definitions

The gt method is a special method that implements the “greater than” operator (>) in Python. It allows objects to define their own comparison behavior when used with the > operator.

Key characteristics: it takes two parameters (self and other), returns a boolean value, and should return NotImplemented for unsupported comparisons. It’s part of Python’s rich comparison methods.

Basic gt Implementation

Here’s a simple implementation showing how gt works with a custom class. This example compares objects based on an attribute value.

basic_gt.py

class Product: def init(self, name, price): self.name = name self.price = price

def __gt__(self, other):
    if not isinstance(other, Product):
        return NotImplemented
    return self.price > other.price

p1 = Product(“Laptop”, 999) p2 = Product(“Phone”, 699) print(p1 > p2) # True

This example compares Product instances based on their price attribute. The gt method returns True if the current instance’s price is greater than the other’s price.

The NotImplemented return value indicates when comparison with unsupported types is attempted, allowing Python to try the reverse operation.

Comparing Different Types

gt can handle comparisons between different types, though it’s good practice to return NotImplemented for unsupported types.

different_types.py

class Distance: def init(self, meters): self.meters = meters

def __gt__(self, other):
    if isinstance(other, Distance):
        return self.meters > other.meters
    elif isinstance(other, (int, float)):
        return self.meters > other
    return NotImplemented

d1 = Distance(100) print(d1 > Distance(50)) # True print(d1 > 75) # True print(d1 > “100”) # TypeError

This Distance class can compare with other Distance objects or numbers. When compared with an unsupported type like string, it returns NotImplemented, leading to a TypeError.

The method first checks the type of other before performing the comparison, making it more flexible while maintaining type safety.

Reverse Comparison with lt

When gt returns NotImplemented, Python tries the reverse operation using the other object’s lt method.

reverse_comparison.py

class Temperature: def init(self, celsius): self.celsius = celsius

def __gt__(self, other):
    if isinstance(other, Temperature):
        return self.celsius > other.celsius
    return NotImplemented

def __lt__(self, other):
    if isinstance(other, (int, float)):
        return self.celsius < other
    return NotImplemented

t = Temperature(25) print(t > Temperature(20)) # True (uses gt) print(30 > t) # True (uses lt)

This example shows how Python falls back to lt when gt isn’t implemented for a particular comparison. The 30 > t expression uses t.lt(30).

Implementing both methods provides more flexible comparison behavior while maintaining consistency between operations.

Inheritance and gt

When using inheritance, gt can be overridden to modify comparison behavior in subclasses while maintaining the parent’s functionality.

inheritance.py

class Animal: def init(self, weight): self.weight = weight

def __gt__(self, other):
    if not isinstance(other, Animal):
        return NotImplemented
    return self.weight > other.weight

class Dog(Animal): def gt(self, other): if isinstance(other, Dog): return self.weight * 2 > other.weight * 2 return super().gt(other)

a1 = Animal(10) a2 = Animal(15) d1 = Dog(5) d2 = Dog(8)

print(a1 > a2) # False print(d1 > d2) # False (but compares 10 vs 16) print(d1 > a1) # False (uses Animal.gt)

The Dog class modifies comparison behavior when comparing two Dog instances but falls back to the parent class’s gt for other comparisons.

This pattern allows specialized comparison logic while maintaining consistent behavior with the parent class and other types.

Total Ordering with functools

The functools.total_ordering decorator can generate missing comparison methods if at least one comparison method (like gt) and eq are defined.

total_ordering.py

from functools import total_ordering

@total_ordering class Score: def init(self, points): self.points = points

def __gt__(self, other):
    if not isinstance(other, Score):
        return NotImplemented
    return self.points > other.points

def __eq__(self, other):
    if not isinstance(other, Score):
        return NotImplemented
    return self.points == other.points

s1 = Score(85) s2 = Score(90) print(s1 > s2) # False print(s1 <= s2) # True (generated by total_ordering)

With just gt and eq defined, the decorator provides all other comparison methods (lt, le, etc.). This reduces boilerplate code.

The generated methods maintain consistent behavior with the defined comparisons, ensuring all operations work as expected based on the two implemented methods.

Best Practices

• Return NotImplemented for unsupported types: Allows Python to try reverse operations

• Maintain consistency: Ensure gt and lt are consistent

• Implement eq: For complete comparison functionality

• Consider total_ordering: When implementing multiple comparisons

• Document behavior: Clearly document comparison logic and supported types

Source References

• Python gt Documentation

• functools.total_ordering Docs

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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