#SqrtAssert.py
""" Shows how the assert statement can be used to check
that the preconditions of a function are satisfied
and that what it returns "lives up to" the specifications.
"""

def sqrt(x):
   """ Returns an approximate square root of x in that
   |x - sqrt(x)**2| <= .000001
   
   PreC: x is a positive number.
   """
   
   assert x>0, 'The sqrt function requires a positive argument.'
   
   L=float(x);  
   for k in range(10):
      L = (L+x/L)/2
      
   assert abs(L*L-x)<=10**(-6), 'Inaccurate Square Root'
   return L

if __name__ == '__main__':
    x  = input('Enter a positive number: ')
    z = sqrt(x)
    print 'sqrt(%5.3f) = %10.6f' % (x,z)