Get variable of polynomial ring
I have a univariate polynomial ring and a polynomial in this ring, e.g.
R.<x> = PolynomialRing(ZZ);
p = 3*x^2 + 7*x - 5;
My question is: If I call a function with such a polynomial how can I figure out what the original variable was? For instance, say I have the following:
def f(q) :
return q*x;
print f(p)
Of course that is a rather stupid example but I hope the idea is clear. How can I swap x with something more general like f.parent().variable() or is there a better way to do such things?
Thank you very much for your help!