From 923e9ab90d783580b5b0bafacb88fb57a06bc87a Mon Sep 17 00:00:00 2001
From: Ulysses Tiberious <ulysses.tiberious@gmail.com>
Date: Mon, 30 Mar 2026 00:39:00 +0800
Subject: [PATCH] Make Pdop and Sdop hashable and improve SymPy integration

Add __hash__ and __ne__ methods to Pdop and Sdop classes so they can
be used in sets, dictionaries, and other contexts that require hashable
objects. This is a step toward better integration with SymPy's
expression system.

Fixes utiberious/galgebra#8
---
 galgebra/dop.py               | 15 +++++++++++++++
 test/test_differential_ops.py | 26 ++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/galgebra/dop.py b/galgebra/dop.py
index 19f3226e..aa2f04d3 100644
--- a/galgebra/dop.py
+++ b/galgebra/dop.py
@@ -231,6 +231,15 @@ def __eq__(self, other):
         else:
             return NotImplemented
 
+    def __ne__(self, other):
+        result = self.__eq__(other)
+        if result is NotImplemented:
+            return result
+        return not result
+
+    def __hash__(self):
+        return hash(self.terms)
+
     def __add__(self, sdop):
         return Sdop.Add(self, sdop)
 
@@ -312,6 +321,12 @@ def __eq__(self, A):
                 return True
             return False
 
+    def __ne__(self, A):
+        return not self.__eq__(A)
+
+    def __hash__(self):
+        return hash(tuple(sorted(self.pdiffs.items())))
+
     def __init__(self, __arg):
         """
         The partial differential operator is a partial derivative with
diff --git a/test/test_differential_ops.py b/test/test_differential_ops.py
index 33a848fc..dcf2ea91 100644
--- a/test/test_differential_ops.py
+++ b/test/test_differential_ops.py
@@ -311,6 +311,32 @@ def test_multiply(self):
             with pytest.raises(TypeError):
                 op(p, ex)
 
+    def test_hash_and_eq(self):
+        """Test Pdop/Sdop are hashable and support ne (issue 234)."""
+        x, y = symbols('x y', real=True)
+        p1 = Pdop(x)
+        p2 = Pdop(y)
+        p1b = Pdop(x)
+        p0 = Pdop({})
+
+        # Pdop is hashable
+        assert hash(p1) == hash(p1b)
+        assert {p1, p2, p1b} == {p1, p2}
+
+        # ne works
+        assert p1 != p2
+        assert not (p1 != p1b)
+
+        # identity pdop
+        assert p0 == S.One
+        assert p0 != p1
+
+        # Sdop is hashable
+        s1 = Sdop([(x, p1)])
+        s2 = Sdop([(y, p2)])
+        assert hash(s1) is not None
+        assert {s1, s2} == {s1, s2}
+
     def test_constructor_errors(self):
         # not a symbol or dict
         with pytest.raises(TypeError, match='dictionary or symbol is required'):