# Strange type error in interactive

I'm trying to make a simple interactive for my students to practice differentiating polynomials. For some reason, when an answer is entered, Sage tries to convert it (a polynomial) to an instance of sage.structure.parent.Parent and chokes. The same code run outside of an interactive works fine. Why is Sage trying to do this conversion and how do I get it to stop?

#Create polynomial generator
poly.<x>=PolynomialRing(QQ)

#Problems correct (in a row and total)
streak = 0
tot = 0
first = True

@interact
def polyDiff(ans=input_box(label="f'(x)=", type=sage.rings.polynomial.polynomial_rational_flint.Polynomial_rational_flint)):
global streak
global tot
global first

global poly

#Set up and display problem on first run
if (first == True):
rand_poly=poly.random_element(2)
first = False
html("f(x)=")+html(rand_poly)

corr = diff(rand_poly, x)

if (ans is not None):
if (corr == ans):
print "Correct!"
tot += 1
streak += 1
#Generate new problem
rand_poly = poly.random_element(5)
else:
html("Try again")
streak = 0
else:

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type=sage.rings.polynomial.polynomial_rational_flint.Polynomial_rational_flint


I had to set (don't know why)

global rand_poly


to get it work

A further suggestion (looks better):

html.table([("$f(x)=$",rand_poly)])

more

Thanks! That works. (Note to anyone wanting to use this code: move the display line to the end of the function to get the interactive to update correctly after the first problem.)

1

Even better: [Sage tables](http://sagemath.org/doc/reference/misc/sage/misc/table.html?highlight=table#sage.misc.table.table) are now a top-level thing.