Enable sympy-symengine round-trip for Dummy

Author: bjodah

symengine/lib/symengine.pxd

@@ -323,6 +323,7 @@ cdef extern from "<symengine/basic.h>" namespace "SymEngine":
     rcp_const_basic make_rcp_Symbol "SymEngine::make_rcp<const SymEngine::Symbol>"(string name) nogil
     rcp_const_basic make_rcp_Dummy "SymEngine::make_rcp<const SymEngine::Dummy>"() nogil
     rcp_const_basic make_rcp_Dummy "SymEngine::make_rcp<const SymEngine::Dummy>"(string name) nogil
+    rcp_const_basic make_rcp_Dummy "SymEngine::make_rcp<const SymEngine::Dummy>"(string name, size_t index) nogil
     rcp_const_basic make_rcp_PySymbol "SymEngine::make_rcp<const SymEngine::PySymbol>"(string name, PyObject * pyobj, bool use_pickle) except +
     rcp_const_basic make_rcp_Constant "SymEngine::make_rcp<const SymEngine::Constant>"(string name) nogil
     rcp_const_basic make_rcp_Infty "SymEngine::make_rcp<const SymEngine::Infty>"(RCP[const Number] i) nogil

symengine/lib/symengine_wrapper.in.pyx

@@ -278,10 +278,10 @@ def sympy2symengine(a, raise_error=False):
     """
     import sympy
     from sympy.core.function import AppliedUndef as sympy_AppliedUndef
-    if isinstance(a, sympy.Symbol):
+    if isinstance(a, sympy.Dummy):
+        return Dummy(a.name, a.dummy_index)
+    elif isinstance(a, sympy.Symbol):
         return Symbol(a.name)
-    elif isinstance(a, sympy.Dummy):
-        return Dummy(a.name)
     elif isinstance(a, sympy.Mul):
         return mul(*[sympy2symengine(x, raise_error) for x in a.args])
     elif isinstance(a, sympy.Add):
@@ -1337,15 +1337,18 @@ cdef class Symbol(Expr):
 
 cdef class Dummy(Symbol):
 
-    def __init__(Basic self, name=None, *args, **kwargs):
-        if name is None:
-            self.thisptr = symengine.make_rcp_Dummy()
+    def __init__(Basic self, name=None, dummy_index=None, *args, **kwargs):
+        if dummy_index is None:
+            if name is None:
+                self.thisptr = symengine.make_rcp_Dummy()
+            else:
+                self.thisptr = symengine.make_rcp_Dummy(name.encode("utf-8"))
         else:
-            self.thisptr = symengine.make_rcp_Dummy(name.encode("utf-8"))
+            self.thisptr = symengine.make_rcp_Dummy(name.encode("utf-8"), dummy_index)
 
     @property
     def name(self):
-        return self.__str__()[1:]
+        return self.__str__()
 
     def _sympy_(self):
         import sympy

symengine/tests/test_pickling.py

@@ -1,4 +1,4 @@
-from symengine import symbols, sin, sinh, have_numpy, have_llvm, cos, Symbol
+from symengine import symbols, sin, sinh, have_numpy, have_llvm, cos, Symbol, Dummy
 from symengine.test_utilities import raises
 import pickle
 import unittest
@@ -57,3 +57,17 @@ def test_llvm_double():
     ll = pickle.loads(ss)
     inp = [1, 2, 3]
     assert np.allclose(l(inp), ll(inp))
+
+
+def _check_pickling_roundtrip(arg):
+    s2 = pickle.dumps(arg)
+    arg2 = pickle.loads(s2)
+    assert arg == arg2
+    s3 = pickle.dump(arg2)
+    arg3 = pickle.loads(s3)
+    assert arg == arg3
+
+def test_pickling_roundtrip():
+    x, y, z = symbols('x y z')
+    _check_pickling_roundtrip(x+y)
+    _check_pickling_roundtrip(Dummy('d'))

symengine/tests/test_sympy_conv.py

@@ -1,6 +1,6 @@
 from symengine import (Symbol, Integer, sympify, SympifyError, log,
         function_symbol, I, E, pi, oo, zoo, nan, true, false,
-        exp, gamma, have_mpfr, have_mpc, DenseMatrix, sin, cos, tan, cot,
+        exp, gamma, have_mpfr, have_mpc, DenseMatrix, Dummy, sin, cos, tan, cot,
         csc, sec, asin, acos, atan, acot, acsc, asec, sinh, cosh, tanh, coth,
         asinh, acosh, atanh, acoth, atan2, Add, Mul, Pow, diff, GoldenRatio,
         Catalan, EulerGamma, UnevaluatedExpr, RealDouble)
@@ -833,3 +833,24 @@ def test_conv_large_integers():
     if have_sympy:
         c = a._sympy_()
         d = sympify(c)
+
+def _check_sympy_roundtrip(arg):
+    arg_sy1 = sympy.sympify(arg)
+    arg_se2 = sympify(arg_sy1)
+    print(f"{type(arg)=} {type(arg_se2)=}")
+    assert arg == arg_se2
+    arg_sy2 = sympy.sympify(arg_se2)
+    assert arg_sy2 == arg_sy1
+    arg_se3 = sympify(arg_sy2)
+    assert arg_se3 == arg
+
+
+@unittest.skipIf(not have_sympy, "SymPy not installed")
+def test_sympy_roundtrip():
+    x = Symbol("x")
+    y = Symbol("y")
+    d = Dummy("d")
+    _check_sympy_roundtrip(x)
+    _check_sympy_roundtrip(x+y)
+    _check_sympy_roundtrip(x**y)
+    _check_sympy_roundtrip(d)