little fun creating a square root function

sqrt.py

#!/usr/bin/env python
################################################################################
# The MIT License (MIT)
#
# Copyright (c) 2018 Mark LaPerriere
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
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# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
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# The above copyright notice and this permission notice shall be included in
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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################################################################################
from __future__ import print_function

PRECISION_DIGITS = 10
PRECISION = 1.0 / (10 ** PRECISION_DIGITS)
print("Find the square root to {} decimals".format(PRECISION))

def sqrt_(a):
    n = a
    if n < 0:
        n /= -1
    
    g = int(n)
    i = 0
    while (g*g > n):
        g = g >> 1
        i += 1

    print("{0} guess (took {1} reductions): {2}".format(a, i, g))

    while (not (-PRECISION < (g*g-n) < PRECISION)):
        g = (g + (n / g)) / 2

    return float(round(g, PRECISION_DIGITS))

    
print(sqrt_(10))        # 3.1622776602
print(sqrt_(-25))       # 5.0
print(sqrt_(9))         # 3.0
print(sqrt_(100))       # 10.0
print(sqrt_(4))         # 2.0
print(sqrt_(21))        # 4.582575695
print(sqrt_(716044081)) # 26759.0