Code example missing statement p 50

[dgrunberg]

The 2 code examples for the iterative square root algorithm cause an 'UnboundLocalError' and are missing an assignment; even with local vars initialized, the loop will never terminate as x is never updated.

I agree the use of math.inf is messy but prevents an extra check in the while loop like while x is None or abs()>.01

These are on line approx 644 of chapter1.md (p50 of the un-numbered chapter of the pdf book), and then again 3 paragraphs later.

import math
def sqrt(a: float) -> float:
    x = math.inf                         #Need to avoid UboundLocalError, x is previous value, x_n is current value
    x_n = a / 2 # initial guess
    while abs(x_n - x) > 0.01:
        x = x_n                             #<== missing                
        x_n = (x + (a / x)) / 2
    return x_n