only one attr dict in vdom constructor

this allows for some minor performance and logical
optimizations that simplifies things slightly

Author: rmorshea

src/idom/core/vdom.py

@@ -5,7 +5,7 @@
 
 from __future__ import annotations
 
-from typing import Any, Dict, Iterable, List, Mapping, Optional, Sequence, Tuple, Union
+from typing import Any, Iterable, List, Mapping, Optional, Sequence, Tuple, Union
 
 from fastjsonschema import compile as compile_json_schema
 from mypy_extensions import TypedDict
@@ -119,10 +119,9 @@ def vdom(
         tag:
             The type of element (e.g. 'div', 'h1', 'img')
         attributes_and_children:
-            Attribute mappings followed by iterables of children for the element. The
-            attributes **must** precede the children, though you may pass multiple sets
-            of attributes, or children which will be merged into their respective parts
-            of the model.
+            An optional attribute mapping followed by any number of children or
+            iterables of children. The attribute mapping **must** precede the children,
+            or children which will be merged into their respective parts of the model.
         key:
             A string idicating the identity of a particular element. This is significant
             to preserve event handlers across updates - without a key, a re-render would
@@ -201,26 +200,22 @@ def constructor(
 
 
 def coalesce_attributes_and_children(
-    attributes_and_children: _AttributesAndChildrenArg,
-) -> Tuple[Dict[str, Any], List[Any]]:
-    attributes: Dict[str, Any] = {}
-    children: List[Any] = []
+    values: Sequence[Any],
+) -> Tuple[Mapping[str, Any], List[Any]]:
+    if not values:
+        return {}, []
+
+    children_or_iterables: Sequence[Any]
+    attributes, *children_or_iterables = values
+    if not isinstance(attributes, Mapping) or "tagName" in attributes:
+        attributes = {}
+        children_or_iterables = values
 
-    began_children = False
-    for argument in attributes_and_children:
-        if isinstance(argument, Mapping):
-            if "tagName" not in argument:
-                if began_children:
-                    raise ValueError("Attribute dictionaries should precede children.")
-                attributes.update(argument)
-            else:
-                children.append(argument)
-                began_children = True
-        elif not isinstance(argument, str) and isinstance(argument, Iterable):
-            children.extend(argument)
-            began_children = True
+    children: List[Any] = []
+    for child in children_or_iterables:
+        if isinstance(child, (str, Mapping)) or not hasattr(child, "__iter__"):
+            children.append(child)
         else:
-            children.append(argument)
-            began_children = True
+            children.extend(child)
 
     return attributes, children

tests/test_core/test_vdom.py

@@ -32,25 +32,6 @@ async def handler(event):
                 "children": [{"tagName": "div"}, 1, {"tagName": "div"}, 2],
             },
         ),
-        (
-            # multiple dictionaries of attributes are merged
-            idom.vdom("div", {"width": "30px"}, {"height": "20px"}),
-            {"tagName": "div", "attributes": {"width": "30px", "height": "20px"}},
-        ),
-        (
-            idom.vdom(
-                "div",
-                {"width": "30px"},
-                {"height": "20px"},
-                [idom.vdom("div"), 1],
-                (idom.vdom("div"), 2),
-            ),
-            {
-                "tagName": "div",
-                "children": [{"tagName": "div"}, 1, {"tagName": "div"}, 2],
-                "attributes": {"width": "30px", "height": "20px"},
-            },
-        ),
         (
             idom.vdom("div", event_handlers=fake_events),
             {"tagName": "div", "eventHandlers": fake_events},
@@ -96,11 +77,6 @@ def test_simple_node_construction(actual, expected):
     assert actual == expected
 
 
-def test_vdom_attribute_arguments_come_before_children():
-    with pytest.raises(ValueError):
-        idom.vdom("div", ["c1", "c2"], {"attr": 1})
-
-
 def test_make_vdom_constructor():
     elmt = make_vdom_constructor("some-tag")