Bellard's formula for calculating PI in Python

bellard.py

import sys
from decimal import Decimal, getcontext

k = int(sys.argv[1]) if len(sys.argv) > 1 else 70

def bellard(n):
  getcontext().prec = n + 1
  return Decimal(1.0/(2**6)) * sum([Decimal(-1)**k/(1024**k) * (Decimal(256)/(10*k+1) + Decimal(1)/(10*k+9) - Decimal(64)/(10*k+3) - Decimal(32)/(4*k+1) - Decimal(4)/(10*k+5) - Decimal(4)/(10*k+7) - Decimal(1)/(4*k+3)) for k in range(n)])

print(bellard(k))

You use k in bellard(n), rather than n. This causes errors if the function is called in any other context than with k and inside bellard.py

Actually, I was wrong. I missed that you used k as in for k in range(n).