title: Does `continued_fraction(d)` for a quadratic field element d compute whole preperiod and period eagerly?
body: <p>New to sage, toying with continued fractions. I noticed that my code experiences performance degradation when I use <code>continued_fraction(d)</code>, where d is represented as a <code>QuadraticField</code> element, and the CF has long period (in the thousands). There is no slowness if the same value is represented as a regular <code>sage.symbolic.expression.Expression</code>.</p>
  <p>Does sage compute the preperiod and period eagerly for elements of quadratic fields? Am I better off not using QuadraticField values if all I need is a constant number of first partial quotients regardless of period length?</p>