Stop using pybind's implicit __hash__ (closes gh-102)

gen_wrap.py

@@ -1370,6 +1370,10 @@ def write_wrapper(outf, meth):
 
 # {{{ exposer generator
 
+def is_hash(meth):
+    return meth.name == "get_hash" and len(meth.args) == 1
+
+
 def write_exposer(outf, meth, arg_names, doc_str):
     func_name = f"isl::{meth.cls}_{meth.name}"
     py_name = meth.name
@@ -1385,7 +1389,7 @@ def write_exposer(outf, meth, arg_names, doc_str):
     if meth.name == "size" and len(meth.args) == 1:
         py_name = "__len__"
 
-    if meth.name == "get_hash" and len(meth.args) == 1:
+    if is_hash(meth):
         py_name = "__hash__"
 
     extra_py_names = []
@@ -1509,6 +1513,16 @@ def gen_wrapper(include_dirs, include_barvinok=False, isl_version=None):
             for cls in classes
             for meth in fdata.classes_to_methods.get(cls, [])])
 
+        for cls in classes:
+            has_isl_hash = any(
+                    is_hash(meth) for meth in fdata.classes_to_methods.get(cls, []))
+
+            if not has_isl_hash:
+                # pybind11's C++ object base class has an object identity
+                # __hash__ that everyone inherits automatically. We don't
+                # want that.
+                expf.write(f'wrap_{cls}.attr("__hash__") = py::none();\n')
+
         expf.close()
         wrapf.close()
 

islpy/__init__.py

@@ -313,9 +313,6 @@ def generic_repr(self):
             cls.__str__ = generic_str
             cls.__repr__ = generic_repr
 
-        if not hasattr(cls, "__hash__"):
-            raise AssertionError(f"not hashable: {cls}")
-
     # }}}
 
     # {{{ Python set-like behavior
@@ -599,15 +596,26 @@ def basic_obj_get_constraints(self):
         self.foreach_constraint(result.append)
         return result
 
+
     # {{{ BasicSet
 
+    def basic_set_hash(self):
+        return hash((type(self), Set.from_basic_set(self)))
+
     BasicSet.get_constraints = basic_obj_get_constraints
+    assert BasicSet.__hash__  is None
+    BasicSet.__hash__ = basic_set_hash
 
     # }}}
 
     # {{{ BasicMap
 
+    def basic_map_hash(self):
+        return hash((type(self), Map.from_basic_map(self)))
+
     BasicMap.get_constraints = basic_obj_get_constraints
+    assert BasicMap.__hash__  is None
+    BasicMap.__hash__ = basic_map_hash
 
     # }}}
 

test/test_isl.py

@@ -457,6 +457,15 @@ def test_sched_constraints_set_validity():
     assert str(validity) == str(validity2)
 
 
+def test_basicset_hash():
+    # https://github.com/inducer/islpy/issues/102
+    # isl does not currently (2022-12-30) offer hashing for BasicSet.
+
+    a1 = isl.BasicSet("{[i]: 0<=i<512}")
+    a2 = isl.BasicSet("{[i]: 0<=i<512}")
+    assert hash(a1) == hash(a2)
+
+
 if __name__ == "__main__":
     import sys
     if len(sys.argv) > 1: