polys: remove FracField, make FractionField domain

Partial fix for sympy/sympy#14220

diofant/domains/__init__.py

@@ -14,7 +14,6 @@
 from . import gmpyrationalfield  # noqa: F401
 from . import algebraicfield  # noqa: F401
 from . import polynomialring  # noqa: F401
-from . import fractionfield  # noqa: F401
 from . import expressiondomain  # noqa: F401
 
 from .domain import Domain  # noqa: F401
@@ -31,7 +30,6 @@
 from .gmpyrationalfield import GMPYRationalField
 from .algebraicfield import AlgebraicField  # noqa: F401
 from .polynomialring import PolynomialRing  # noqa: F401
-from .fractionfield import FractionField  # noqa: F401
 from .expressiondomain import ExpressionDomain
 from .groundtypes import PythonRational  # noqa: F401
 

diofant/domains/domain.py

@@ -277,7 +277,7 @@ def poly_ring(self, *symbols, **kwargs):
 
     def frac_field(self, *symbols, **kwargs):
         """Returns a fraction field, i.e. `K(X)`. """
-        from .fractionfield import FractionField
+        from ..polys.fields import FractionField
         return FractionField(self, symbols, kwargs.get("order", lex))
 
     def is_one(self, a):

diofant/domains/polynomialring.py

@@ -102,11 +102,11 @@ def from_FractionField(self, a, K0):
         denom = K0.denom(a)
 
         if denom.is_ground:
-            return self.from_PolynomialRing(K0.numer(a)/denom, K0.field.ring.to_domain())
+            return self.from_PolynomialRing(K0.numer(a)/denom, K0.ring.to_domain())
 
     def get_field(self):
         """Returns a field associated with `self`. """
-        return self.ring.to_field().to_domain()
+        return self.ring.to_field()
 
     def is_positive(self, a):
         """Returns True if `LC(a)` is positive. """

diofant/domains/tests/test_domains.py

@@ -685,9 +685,9 @@ def test_PolynomialRing_from_FractionField():
     g = (x**2 + y**2)/4
     h = x**2 + y**2
 
-    assert R.to_domain().from_FractionField(f, F.to_domain()) is None
-    assert R.to_domain().from_FractionField(g, F.to_domain()) == X**2/4 + Y**2/4
-    assert R.to_domain().from_FractionField(h, F.to_domain()) == X**2 + Y**2
+    assert R.to_domain().from_FractionField(f, F) is None
+    assert R.to_domain().from_FractionField(g, F) == X**2/4 + Y**2/4
+    assert R.to_domain().from_FractionField(h, F) == X**2 + Y**2
 
     F,  x, y = field("x,y", QQ)
     R,  X, Y = ring("x,y", QQ)
@@ -696,9 +696,9 @@ def test_PolynomialRing_from_FractionField():
     g = (x**2 + y**2)/4
     h = x**2 + y**2
 
-    assert R.to_domain().from_FractionField(f, F.to_domain()) is None
-    assert R.to_domain().from_FractionField(g, F.to_domain()) == X**2/4 + Y**2/4
-    assert R.to_domain().from_FractionField(h, F.to_domain()) == X**2 + Y**2
+    assert R.to_domain().from_FractionField(f, F) is None
+    assert R.to_domain().from_FractionField(g, F) == X**2/4 + Y**2/4
+    assert R.to_domain().from_FractionField(h, F) == X**2 + Y**2
 
 
 def test_FractionField_from_PolynomialRing():
@@ -708,17 +708,17 @@ def test_FractionField_from_PolynomialRing():
     f = 3*x**2 + 5*y**2
     g = x**2/3 + y**2/5
 
-    assert F.to_domain().from_PolynomialRing(f, R.to_domain()) == 3*X**2 + 5*Y**2
-    assert F.to_domain().from_PolynomialRing(g, R.to_domain()) == (5*X**2 + 3*Y**2)/15
+    assert F.from_PolynomialRing(f, R.to_domain()) == 3*X**2 + 5*Y**2
+    assert F.from_PolynomialRing(g, R.to_domain()) == (5*X**2 + 3*Y**2)/15
 
     RALG,  u, v = ring("u,v", ALG)
     pytest.raises(CoercionFailed,
-                  lambda: F.to_domain().convert(3*u**2 + 5*sqrt(2)*v**2))
+                  lambda: F.convert(3*u**2 + 5*sqrt(2)*v**2))
 
 
 def test_FractionField_convert():
     F,  X, Y = field("x,y", QQ)
-    F.to_domain().convert(QQ_python()(1, 3)) == F.one/3
+    F.convert(QQ_python()(1, 3)) == F.one/3
 
 
 def test_FF_of_type():

diofant/polys/__init__.py

@@ -42,4 +42,4 @@
 from .partfrac import apart, apart_list, assemble_partfrac_list  # noqa: F401
 from .polyoptions import Options  # noqa: F401
 from .rings import ring, sring, vring  # noqa: F401,F403
-from .fields import field, sfield, vfield  # noqa: F401
+from .fields import FractionField, field, vfield  # noqa: F401