How to calculate pi to the 1000 digit with python 2.7?

Question

I want to caculate pi to a big digit in python 2, but the code doesn't work - it just closes and I want to see how long it takes.

from decimal import Decimal, getcontext
from time import time, strftime
import datetime

def arccot(x, digits):
    getcontext().prec = digits
    total = 0
    n = 1  
    while Decimal((2 * n - 1) * x ** (2 * n - 1)) < Decimal(10 ** digits):
        term = ((-1)**(n - 1)) * 1 / Decimal((2 * n - 1) * x ** (2 * n - 1))
        total += term
        n += 1
    return total

def pi(decimals):
    timestart = time()
    print "pi = " + str(Decimal(4 * (4 * arccot(5, decimals + 3) - arccot(239,
        decimals + 3))).quantize(Decimal(10) ** (-decimals)))
    timeelapsedint = round(time() - timestart, 2)
    timeelapsedstr = str(datetime.timedelta(seconds = round(
        timeelapsedint, 0)))
    print "runtime: " + timeelapsedstr + " or " + str(
        timeelapsedint) + " seconds."

Your code has no top-level driver. All it does is define two functions and quit. You never call your functions. — Prune, Feb 07 '19 at 17:32
All you need to do is add the line `pi(1000)` to the end of the script and it will work. — ekhumoro, Feb 07 '19 at 18:00
What closes? How are you running the script and on what platform? — ekhumoro, Feb 07 '19 at 18:04
i save the file as filename.py and i downloaded python 2.7 for windows10 and when i save it I click the file and it stays open for a little bit but dont display any text then it just closes the file called filename.py — coder, Feb 07 '19 at 18:07
Read [this answer](https://stackoverflow.com/a/1527012/984421) about running python scripts on windows. — ekhumoro, Feb 07 '19 at 18:10

Jeppe · Accepted Answer · 2019-02-07T17:41:05.710

Just call your function (notice the last line):

# Pi Calculator

# Python 2.7.3

# After running, type "pi(n)" where n is the number of decimals for pi.  For

#  example, if you would like to calculate 100 decimals for pi, type "pi(100)".



# import python libraries

from decimal import Decimal, getcontext

from time import time, strftime

import datetime

# arccot function using power formula arccot = 1/x - 1/(3x^3) + 1/(5x^5) ...

def arccot(x, digits):

    # set precision and starting values

    getcontext().prec = digits

    total = 0
    n = 1

    # loop while new term is large enough to actually change the total

    while Decimal((2 * n - 1) * x ** (2 * n - 1)) < Decimal(10 ** digits):

        # find value of new term

        term = ((-1)**(n - 1)) * 1 / Decimal((2 * n - 1) * x ** (2 * n - 1))

        # add the new term to the total

        total += term

        # next n

        n += 1

    # return the sum

    return total



# pi function

def pi(decimals):

    # start timer

    timestart = time()

    # find pi using Machin's Formula pi = 4 * (4 * arccot(5) - arccot(239))

    #  and the power formula for arccot (see arccot function above)
    print "pi = " + str(Decimal(4 * (4 * arccot(5, decimals + 3) - arccot(239, decimals + 3))).quantize(Decimal(10) ** (-decimals)))



    # display elapsed time

    timeelapsedint = round(time() - timestart, 2)

    timeelapsedstr = str(datetime.timedelta(seconds = round(timeelapsedint, 0)))

    print "runtime: " + timeelapsedstr + " or " + str(timeelapsedint) + " seconds."

pi(1000)

Outputs:

pi = 3.14159265358979323....more digits
runtime: 0:00:00 or 0.22 seconds.

Also, your code is not properly formatted, but I can't edit it. My snippet here is formatted properly.

@coder Did you add the call to `pi(1000)` after the two functions? How are you running it? — Jeppe, Feb 07 '19 at 17:42
Well technically speaking, if you run it as is, it won't do anything as you're not printing the value — Peter, Feb 07 '19 at 17:43
i run it by opening it with python 2.7.3 and i copied all the code you wrote and pasting it in the file — coder, Feb 07 '19 at 17:44
@Peter What do you mean? The function `pi` doesn't return a value - it calculates it and prints it. — Jeppe, Feb 07 '19 at 17:46
@Jeppe My bad haha, I just saw "not outputting anything" combined with not printing the function result, and assumed it was that without actually reading the code :p — Peter, Feb 08 '19 at 01:28

How to calculate pi to the 1000 digit with python 2.7?

1 Answers1