Raise errors for invalid attributes directly on __call__.

This commit transforms attributes to strings directly when being called
rather at rendering time. This makes exceptions for invalid attributes
appear directly leading to clearer stack traces.

Fixes #49.

docs/changelog.md

@@ -1,5 +1,8 @@
 # Changelog
 
+## next
+- Raise errors directly on invalid attributes. This avoids cryptic stack traces for invalid attributes. [Issue #49](https://github.com/pelme/htpy/issues/49) [PR #55](https://github.com/pelme/htpy/pull/55).
+
 ## 24.8.3 - 2024-08-28
 - Support passing htpy elements directly to Starlette responses. Document Starlette support. [PR #50](https://github.com/pelme/htpy/pull/50).
 - Allow passing ints to attributes and children [PR #52](https://github.com/pelme/htpy/pull/52).

examples/bad_attribute.py

@@ -0,0 +1,20 @@
+from htpy import div
+
+
+def good_component_a():
+    return div[good_component_b()]
+
+
+def good_component_b():
+    return div[good_component_c()]
+
+
+def good_component_c():
+    return div[bad_component()]
+
+
+def bad_component():
+    return div(a=object())
+
+
+print(str(good_component_a()))

htpy/__init__.py

@@ -213,11 +213,9 @@ def __getattr__(name: str) -> Element:
 class BaseElement:
     __slots__ = ("_name", "_attrs", "_children")
 
-    def __init__(
-        self, name: str, attrs: dict[str, Attribute] | None = None, children: Node = None
-    ) -> None:
+    def __init__(self, name: str, attrs_str: str = "", children: Node = None) -> None:
         self._name = name
-        self._attrs = attrs or {}
+        self._attrs = attrs_str
         self._children = children
 
     def __str__(self) -> _Markup:
@@ -256,19 +254,21 @@ def __call__(self: BaseElementSelf, *args: t.Any, **kwargs: t.Any) -> BaseElemen
 
         return self.__class__(
             self._name,
-            {
-                **(_id_class_names_from_css_str(id_class) if id_class else {}),
-                **attrs,
-                **{_kwarg_attribute_name(k): v for k, v in kwargs.items()},
-            },
+            _attrs_string(
+                {
+                    **(_id_class_names_from_css_str(id_class) if id_class else {}),
+                    **attrs,
+                    **{_kwarg_attribute_name(k): v for k, v in kwargs.items()},
+                }
+            ),
             self._children,
         )
 
     def __iter__(self) -> Iterator[str]:
         return self._iter_context({})
 
     def _iter_context(self, ctx: dict[Context[t.Any], t.Any]) -> Iterator[str]:
-        yield f"<{self._name}{_attrs_string(self._attrs)}>"
+        yield f"<{self._name}{self._attrs}>"
         yield from _iter_node_context(self._children, ctx)
         yield f"</{self._name}>"
 
@@ -301,7 +301,7 @@ def _iter_context(self, ctx: dict[Context[t.Any], t.Any]) -> Iterator[str]:
 
 class VoidElement(BaseElement):
     def _iter_context(self, ctx: dict[Context[t.Any], t.Any]) -> Iterator[str]:
-        yield f"<{self._name}{_attrs_string(self._attrs)}>"
+        yield f"<{self._name}{self._attrs}>"
 
 
 def render_node(node: Node) -> _Markup:

tests/test_attributes.py

@@ -198,4 +198,4 @@ def test_invalid_attribute_key(not_an_attr: t.Any) -> None:
 )
 def test_invalid_attribute_value(not_an_attr: t.Any) -> None:
     with pytest.raises(ValueError, match="Attribute value must be a string"):
-        str(div(foo=not_an_attr))
+        div(foo=not_an_attr)