class_docstr: A class for representing multivariate rational function fields. 
docstr: Convert a polynomial to ``dtype``. 
code: def from_PolynomialRing(K1, a, K0):
      """Convert a polynomial to ``dtype``."""
      if a.is_ground:
          return K1.convert_from(a.coeff(1), K0.domain)
      try:
          return K1.new(a.set_ring(K1.field.ring))
      except (CoercionFailed, GeneratorsError):
          # XXX: We get here if K1=ZZ(x,y) and K0=QQ[x,y]
          # and the poly a in K0 has non-integer coefficients.
          # It seems that K1.new can handle this but K1.new doesn't work
          # when K0.domain is an algebraic field...
          try:
              return K1.new(a)
          except (CoercionFailed, GeneratorsError):
              return None
  
imports: from sympy.polys.domains.compositedomain import CompositeDomain
  from sympy.polys.domains.field import Field
  from sympy.polys.polyerrors import CoercionFailed, GeneratorsError
  from sympy.utilities import public
label_desc: Use image node_id 22 for calling the FractionField obj's underlying member method code with example usage: obj.from_PolynomialRing(K1, a, K0) and returns: K1, K1, K1, None