support.lazy: make __bool__ work.

`if lazy_obj:` didn't work with e.g. `str` because `str.__bool__()` does not exist.
GlasgowEmbedded · Jul 26, 2024 · 346e5c4 · 346e5c4
1 parent 7e26041
commit 346e5c4
Showing 1 changed file with 33 additions and 21 deletions.
diff --git a/software/glasgow/support/lazy.py b/software/glasgow/support/lazy.py
@@ -33,35 +33,47 @@ def __delattr__(self, attr):
         self._force_()
         delattr(self._object_, attr)
 
+    def __bool__(self):
+        self._force_()
+        if self._object_:
+            return True
+        else:
+            return False
+
     def __repr__(self):
         if self._thunk_:
             rep = repr(self._thunk_)
         else:
             rep = repr(self._object_)
         return f"<lazy {rep}>"
 
-    @classmethod
-    def _define_special_(cls, name):
+
+def define_specials():
+    def define_special(name):
         def forward(self, *args, **kwargs):
             self._force_()
             return getattr(self._object_, name)(*args, **kwargs)
         forward.__name__ = name
-        setattr(cls, name, forward)
-
-# See https://docs.python.org/3/reference/datamodel.html#special-lookup
-_specials = [
-    "__str__", "__bytes__", "__format__", "__lt__", "__le__", "__eq__", "__ne__", "__gt__",
-    "__ge__", "__hash__", "__bool__", "__dir__", "__call__", "__len__", "__length_hint__",
-    "__getitem__", "__setitem__", "__delitem__", "__iter__", "__reversed__", "__contains__",
-    "__add__", "__sub__", "__mul__", "__matmul__", "__truediv__", "__floordiv__", "__mod__",
-    "__divmod__", "__pow__", "__lshift__", "__rshift__", "__and__", "__xor__", "__or__",
-    "__radd__", "__rsub__", "__rmul__", "__rmatmul__", "__rtruediv__", "__rfloordiv__", "__rmod__",
-    "__rdivmod__", "__rpow__", "__rlshift__", "__rrshift__", "__rand__", "__rxor__", "__ror__",
-    "__iadd__", "__isub__", "__imul__", "__imatmul__", "__itruediv__", "__ifloordiv__", "__imod__",
-    "__ipow__", "__ilshift__", "__irshift__", "__iand__", "__ixor__", "__ior__", "__neg__",
-    "__pos__", "__abs__", "__invert__", "__complex__", "__int__", "__float__", "__index__",
-    "__round__", "__trunc__", "__floor__", "__ceil__", "__enter__", "__exit__", "__await__",
-    "__aiter__", "__anext__", "__aenter__", "__aexit__"
-]
-for special in _specials:
-    lazy._define_special_(special)
+        setattr(lazy, name, forward)
+
+    # See https://docs.python.org/3/reference/datamodel.html#special-lookup
+    # Note that the loop body has to be in a separate function because of local variable scoping.
+    for name in [
+        "__str__", "__bytes__", "__format__", "__lt__", "__le__", "__eq__", "__ne__", "__gt__",
+        "__ge__", "__hash__", "__dir__", "__call__", "__len__", "__length_hint__",
+        "__getitem__", "__setitem__", "__delitem__", "__iter__", "__reversed__", "__contains__",
+        "__add__", "__sub__", "__mul__", "__matmul__", "__truediv__", "__floordiv__", "__mod__",
+        "__divmod__", "__pow__", "__lshift__", "__rshift__", "__and__", "__xor__", "__or__",
+        "__radd__", "__rsub__", "__rmul__", "__rmatmul__", "__rtruediv__", "__rfloordiv__", "__rmod__",
+        "__rdivmod__", "__rpow__", "__rlshift__", "__rrshift__", "__rand__", "__rxor__", "__ror__",
+        "__iadd__", "__isub__", "__imul__", "__imatmul__", "__itruediv__", "__ifloordiv__", "__imod__",
+        "__ipow__", "__ilshift__", "__irshift__", "__iand__", "__ixor__", "__ior__", "__neg__",
+        "__pos__", "__abs__", "__invert__", "__complex__", "__int__", "__float__", "__index__",
+        "__round__", "__trunc__", "__floor__", "__ceil__", "__enter__", "__exit__", "__await__",
+        "__aiter__", "__anext__", "__aenter__", "__aexit__"
+    ]:
+        define_special(name)
+
+
+define_specials()
+del define_specials