How Can I Accurately Compare Floating-Point Numbers in Python?

Comparing Floating-Point Numbers with Precision in Python

In the realm of programming, comparing floating-point numbers for equality presents challenges. As highlighted by experts like Bruce Dawson, determining equality is complicated by rounding errors and precision limitations.

Is there a Solution in Python?

Python offers a myriad of solutions to this issue. Notably, Python 3.5 introduces the math.isclose and cmath.isclose functions, following the guidance of PEP 485. These functions provide a reliable means of comparing floating-point numbers for approximate equality.

Implementation Details:

import math

# Compare two floating-point numbers for almost-equality
result = math.isclose(0.1, 0.10000000000000001, rel_tol=1e-09, abs_tol=0.0)

Custom Function for Earlier Python Versions:

For Python versions prior to 3.5, the documentation suggests the following custom function:

def isclose(a, b, rel_tol=1e-09, abs_tol=0.0):
    return abs(a-b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol)

Parameters Explained:

• rel_tol: Defines the relative tolerance, adjusting the acceptable difference based on the magnitude of the values being compared.
• abs_tol: Specifies an absolute tolerance, allowing for direct comparison without considering the magnitude of the numbers.

Using either the math.isclose function or the custom function ensures accurate comparison of floating-point numbers for approximate equality, addressing the challenges posed by precision issues.

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