single-assertion 1.0.1

Simple Lightweight library to add pre- and post- conditions as decorators

Single Assertion

This library provides a clean and declarative way to define preconditions and postconditions for functions using decorators, inspired by the principles of Design by Contract. PyPI

Instead of scattering assert statements throughout your code, you can express input and output constraints in a structured and reusable way.

Usage

Going from:

def divideByPositive(a, b):
    assert a >= 0
    assert b >= 0
    if b <= 1:
        result = 0
        
        assert result <= a
        assert result >= 0
        return result
    
    result = a/b
    
    assert result <= a
    assert result >= 0
    return result

to:

from single_assertion import PreCondition, PostCondition

@PreCondition(lambda a: a >= 0, "a")
@PreCondition(lambda b: b >= 0, "b")
@PostCondition(lambda r: r >= 0)
@PostCondition(lambda r, a: r <= a, "a")
def divideByPositive(a, b):
    if b <= 1:
        result = 0
        return result

    result = a / b
    return result

Use class variables by calling self

from single_assertion import PreCondition, PostCondition

class SpecialAdd:

    def __init__(self, a):
        self.a = a

    @PreCondition(lambda self: self.a == 1, "self")
    @PreCondition(lambda b: b == 2, "b")
    def add(self, b):
        return self.a + b

Install

pip install single-assertion