Happy Pi Day! (Codewars Kumite)

README.MD

Calculate Pi to a precision p.

Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (3/14 in the month/day format) since 3, 1, and 4 are the first three significant figures of π. It was founded in 1988 by Larry Shaw, an employee of the San Francisco, California science museum, the Exploratorium.

code.py

import math
from decimal import Decimal as D
from decimal import getcontext


def pi(p=5):
    getcontext().prec = p
    pi = D(0)
    r = 8

    for k in range(10000):
        pi += D(math.pow(r * 2, -k)) * (D(r / 2 / (r * k + 1)) - D(2 / (r * k + 4)) - D(1 / (r * k + 5)) - D(1 / (r * k + 6)))

    return str(pi)

tests.py

import codewars_test as test
import solution # or from solution import example

@test.describe("Pi")
def test_group():
    @test.it("with fixed precision")
    def test_case():
        test.assert_equals(pi(5), "3.1416")
        test.assert_equals(pi(15), "3.14159265358978")
        test.assert_equals(pi(25), "3.141592653589793235602542")
        test.assert_equals(pi(35), "3.1415926535897932356025418121413793")
        test.assert_equals(pi(45), "3.14159265358979323560254181214137928586630673")
        test.assert_equals(pi(55), "3.141592653589793235602541812141379285866306715610149218")
        test.assert_equals(pi(65), "3.1415926535897932356025418121413792858663067156101492186845517866")
        test.assert_equals(pi(85), "3.141592653589793235602541812141379285866306715610149218684551786650252153469632637314")
        test.assert_equals(pi(95), "3.1415926535897932356025418121413792858663067156101492186845517866502521534696326373091178521508")
        test.assert_equals(pi(150), "3.14159265358979323560254181214137928586630671561014921868455178665025215346963263730911785215115971453711742794521158467222631243984205037768560924169")
        test.assert_equals(pi(500), "3.1415926535897932356025418121413792858663067156101492186845517866502521534696326373091178521511597145371174279452115846722263124398420503776856092417015724879565153362564518846533080259991566995294581843769552520010856934537376498001876051239438261699249190309701897707607883013219006243956937026762348649953848128543102206420573056375540865249489600777954999413780342952712043852815772831475875366233547287165743683081215694880350917987858463746449719849593455892649632537572220827114424079726096699")