Python int Method

Last modified April 8, 2025

This comprehensive guide explores Python’s int method, the special method responsible for integer conversion. We’ll cover basic usage, custom implementations, numeric operations, and practical examples.

Basic Definitions

The int method is a special method that defines how an object should be converted to an integer. It is called by the built-in int() function when converting an object to an integer.

Key characteristics: it takes no arguments (except self), must return an integer, and enables objects to participate in integer contexts. It’s part of Python’s numeric protocol alongside float and index.

Basic int Implementation

Here’s a simple class implementing int to demonstrate how objects can define their own integer conversion behavior.

basic_int.py

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

def __int__(self):
    return int(self.meters)

d = Distance(3.7) print(int(d)) # Output: 3

This example shows a Distance class that converts to integer by truncating its meter value. The int() function calls int when applied to a Distance instance.

The implementation simply delegates to Python’s built-in int() conversion of the meters attribute. This is a common pattern for wrapper classes.

Custom Numeric Conversion

int can implement custom conversion logic when simple attribute conversion isn’t sufficient. Here we convert a temperature object.

temperature.py

class Celsius: def init(self, temperature): self.temperature = temperature

def __int__(self):
    return round(self.temperature)

temp = Celsius(36.6) print(int(temp)) # Output: 37

This Celsius class rounds the temperature when converting to integer. The int method provides control over how the conversion happens.

Rounding is often more appropriate than truncation for measurements where precision matters. The method can implement any conversion logic needed.

Currency Conversion Example

For financial applications, int can convert currency objects to their integer value in smallest units (like cents).

currency.py

class Dollar: def init(self, amount): self.amount = amount

def __int__(self):
    return int(self.amount * 100)

price = Dollar(4.99) cents = int(price) print(cents) # Output: 499

This Dollar class converts dollar amounts to cents when cast to integer. The int method multiplies by 100 before conversion.

Financial applications often need this type of conversion for precise arithmetic operations that avoid floating-point rounding errors.

Fraction to Integer Conversion

The int method can implement mathematical operations during conversion, like converting fractions to whole numbers.

fraction.py

class Fraction: def init(self, numerator, denominator): self.numerator = numerator self.denominator = denominator

def __int__(self):
    return self.numerator // self.denominator

half = Fraction(1, 2) print(int(half)) # Output: 0 three_halves = Fraction(3, 2) print(int(three_halves)) # Output: 1

This Fraction class implements integer division when converting to integer. The // operator performs floor division to get the whole number part.

This matches Python’s behavior for built-in numeric types where int() truncates towards zero. The method could implement other rounding if needed.

Custom Object with Multiple Attributes

For complex objects, int can combine multiple attributes into a single integer value based on domain-specific logic.

complex_object.py

class RGBColor: def init(self, red, green, blue): self.red = red self.green = green self.blue = blue

def __int__(self):
    return (self.red << 16) | (self.green << 8) | self.blue

color = RGBColor(255, 128, 0) print(int(color)) # Output: 16744448 (0xFF8000)

This RGBColor class combines three 8-bit color channels into a single 24-bit integer value. Bit shifting combines the components into the standard RGB format.

The int method enables the color to be used in contexts expecting a numeric color value, like some graphics libraries or databases.

Best Practices

• Return proper integers: Always return an actual int, not another type

• Implement related methods: Consider also implementing float if applicable

• Handle edge cases: Decide how to handle None or invalid states

• Document behavior: Clearly document the conversion logic

• Maintain consistency: Ensure int matches other numeric methods

Source References

• Python int Documentation

• Python Numbers ABC

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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