class_docstr: A class for representing multivariate rational function fields. 
docstr: Convert a rational function to ``dtype``. 
code: def from_FractionField(K1, a, K0):
      """Convert a rational function to ``dtype``."""
      try:
          return a.set_field(K1.field)
      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 23 for calling the FractionField obj's underlying member method code with example usage: obj.from_FractionField(K1, a, K0) and returns: a, None