roots.py

import sys


def sqrt(x):
    '''Compute square roots u sing the method of Heron of Alexandria.

    Args:
        x: The number for which the square root is to be computed.

    Returns:
        The square root of x.

    Raises:
        ValueError: If x is negative.
    '''

    if x < 0:
        raise ValueError("Cannot compute square root of negative number {}".format(x))
    guess = x
    i = 0
    while guess * guess != x and i < 20:
        guess = (guess + x / guess) / 2.0
        i += 1
    return guess


def main():
    try:
        print(sqrt(9))
        print(sqrt(2))
        print(sqrt(-1))
    except ValueError as e:
        print(e, file=sys.stderr)

    print("Program execution continues normally here.")

if __name__ == '__main__':
    main()