Covid testing

covidtest.py

import random 
from collections import Counter

class Person:
    
    def __init__(self, issick):
        self.issick = issick

    def __repr__(self):
        if self.issick:
            return f'Sick'
        return f'Healthy'
    
class Population:
    """
    Define a population with sickness prevalence
    """
    def __init__(self, prevalence, size):
        self.prevalence = prevalence
        self.size = size

    def __repr__(self):
        return f'Average # Covid19 patients per million is {1000000 * self.prevalence}'

    def generate(self):
        """
        Population (of size) of `Person`s some with sickness (prevalence)
        """
        for _ in range(self.size):
            if self.prevalence > random.random():
                yield Person(issick=True) 
            else:
                yield Person(issick=False)


class CovidTest:
    
    def __init__(self, true_positive=0.99, true_negative=0.99):
        self.true_positive = true_positive
        self.true_negative = true_negative
        
    def test_person(self, person):
        """
        Test a single person against Covid19
        """
        if person.issick:
            if random.random() < self.true_positive:
                return "True Positive"
            return "False Negative"

        else:
            if random.random() < self.true_negative:
                return "True Negative"
            return "False Positive"
        
    def test_population(self, population):
        """
        Test a population of people (Population object) against Covid19
        """
        test_results = []
        for person in  population.generate():
            result = self.test_person(person)
            test_results.append(result)
        return Counter(test_results)
    
    @staticmethod
    def likelihood(ispositive, population_test):
        """
        If you are tested positive, what is the probability that you are actually sick.
        or vice versa
        
        Args:
            ispositive (bool): True if your test result is positive
            population_test (collections.Counter): Population test results 
        """
        TN = population_test['True Negative']
        FN = population_test['False Negative']
        TP = population_test['True Positive']
        FP = population_test['False Positive']
        
        if ispositive:    
            return f'Likelihood of you are indeed positive is {100 * TP/(FP + TP):.3f}%' 
        return f'Likelihood of you are indeed negative is {100 * TN/(FN + TN):.3f}%'  
            
 

This is a simple simulation of showing how reliable is a finger Covid 19 test for mass

UK = Population(prevalence=0.0002, size=1000000)
covid_test = CovidTest(true_positive=0.98, true_negative=0.98)

pop_test = covid_test.test_population(UK)

>>print(pop_test)
Counter({'True Negative': 979451,
         'False Positive': 20343,
         'True Positive': 203,
         'False Negative': 3})

What is the likelyhood that I'm indeed positive if my test result is positive

covid_test.likelihood(ispositive=True, population_test=pop_test)
>>'Likelihood of you are indeed positive is 0.988%'