Fix/review cleanup (#281)

* fix: replace mutable default argument in dicttoxml()

xml_namespaces had a mutable default dict which is a classic Python
footgun where mutations persist across calls. Changed to None with
an 'or {}' guard inside the function body, matching the pattern
already used in dicttoxml_fast.py.

Amp-Thread-ID: https://ampcode.com/threads/T-019d6bf2-ce86-763d-8c62-08118f358cbe
Co-authored-by: Amp <amp@ampcode.com>

* fix: remove unused Dict and List imports from conftest.py

These typing imports were dead code since the file already uses
the built-in dict[...] and list[...] syntax everywhere.

Amp-Thread-ID: https://ampcode.com/threads/T-019d6bf2-ce86-763d-8c62-08118f358cbe
Co-authored-by: Amp <amp@ampcode.com>

* fix: remove dead setUp/tearDown stubs from TestJson2xml

These were unittest-style no-op methods that serve no purpose in
pytest classes.

Amp-Thread-ID: https://ampcode.com/threads/T-019d6bf2-ce86-763d-8c62-08118f358cbe
Co-authored-by: Amp <amp@ampcode.com>

* fix: hoist SystemRandom() to module level in dicttoxml

Avoids creating a new SystemRandom instance on every make_id() call.
The module-level _SAFE_RANDOM is reused across all invocations.

Amp-Thread-ID: https://ampcode.com/threads/T-019d6bf2-ce86-763d-8c62-08118f358cbe
Co-authored-by: Amp <amp@ampcode.com>

* chore: stop tracking coverage data

* Update json2xml/dicttoxml.py

Co-authored-by: sourcery-ai[bot] <58596630+sourcery-ai[bot]@users.noreply.github.com>

* Align Rust list wrapper semantics with Python

* fix: warnings

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: sourcery-ai[bot] <58596630+sourcery-ai[bot]@users.noreply.github.com>

Author: 3 people

.coverage

@@ -12,6 +12,7 @@
 from defusedxml.minidom import parseString
 
 # Create a safe random number generator
+_SAFE_RANDOM = SystemRandom()
 
 # Set up logging
 LOG = logging.getLogger("dicttoxml")
@@ -29,8 +30,7 @@ def make_id(element: str, start: int = 100000, end: int = 999999) -> str:
     Returns:
         str: The generated ID.
     """
-    safe_random = SystemRandom()
-    return f"{element}_{safe_random.randint(start, end)}"
+    return f"{element}_{_SAFE_RANDOM.randint(start, end)}"
 
 
 def get_unique_id(element: str) -> str:
@@ -641,7 +641,7 @@ def dicttoxml(
     item_wrap: bool = True,
     item_func: Callable[[str], str] = default_item_func,
     cdata: bool = False,
-    xml_namespaces: dict[str, Any] = {},
+    xml_namespaces: dict[str, Any] | None = None,
     list_headers: bool = False,
     xpath_format: bool = False,
 ) -> bytes:
@@ -797,6 +797,8 @@ def dicttoxml(
 
     output = []
     namespace_str = ""
+    if xml_namespaces is None:
+        xml_namespaces = {}
     for prefix in xml_namespaces:
         if prefix == 'xsi':
             for schema_att in xml_namespaces[prefix]:

json2xml/dicttoxml.py

@@ -14,6 +14,8 @@ Default output includes an XML declaration, wraps content in `all`, pretty print
 
 [[json2xml/json2xml.py#Json2xml#to_xml]] calls [[json2xml/dicttoxml.py#dicttoxml]] with the configured wrapper, root, `attr_type`, `item_wrap`, `cdata`, and `list_headers` options. When `item_wrap=False`, list values repeat the parent tag instead of creating `<item>` children. When `pretty=False`, the library returns the serializer bytes directly.
 
+The Rust fast path in [[rust/src/lib.rs#write_dict_contents]] and [[rust/src/lib.rs#write_list_contents]] mirrors those Python list-wrapper rules. `list_headers=True` suppresses the outer list container and repeats the parent tag only for nested dict items, while primitive items still use the same scalar tags that Python emits.
+
 ## XPath 3.1 format
 
 XPath mode swaps the project-specific XML shape for the W3C `json-to-xml` mapping with typed element names and the XPath functions namespace.
@@ -24,4 +26,4 @@ When `xpath_format=True`, [[json2xml/dicttoxml.py#dicttoxml]] delegates payload
 
 Pretty printing acts as a validation step, because the formatter reparses the generated XML before returning it.
 
-[[json2xml/json2xml.py#Json2xml#to_xml]] uses `defusedxml.minidom.parseString` before `toprettyxml`. If the generated bytes are not well-formed XML, the converter raises `InvalidDataError` instead of returning broken pretty output.
+[[json2xml/json2xml.py#Json2xml#to_xml]] uses `defusedxml.minidom.parseString` before `toprettyxml`. If the generated bytes are not well-formed XML, the converter raises `InvalidDataError` instead of returning broken pretty output.

lat.md/behavior.md

@@ -28,4 +28,16 @@ XPath mode should emit the W3C XPath functions namespace and typed child element
 
 ### Item-wrap false repeats parent tag
 
-Disabling item wrapping should repeat the parent element name for primitive list items instead of producing nested `<item>` tags.
+Disabling item wrapping should repeat the parent element name for primitive list items instead of producing nested `<item>` tags.
+
+### Default xml namespaces stay empty
+
+Calling `dicttoxml` without `xml_namespaces` should preserve the legacy root output and avoid adding namespace declarations or `xsi:` attributes implicitly.
+
+### Explicit xml namespaces emit schema attributes
+
+Supplying namespace prefixes and an `xsi` mapping should emit the expected `xmlns:*` declarations plus supported schema attributes without mutating the caller input.
+
+### Xml namespace inputs are not mutated across calls
+
+Reusing one `xml_namespaces` mapping across multiple `dicttoxml` calls should return identical XML each time so namespace declarations never accumulate on the shared dict.

lat.md/tests.md

@@ -340,7 +340,14 @@ fn write_dict_contents(
 
         // Lists in dicts get special wrapping treatment
         if let Ok(list) = val.cast::<PyList>() {
-            if cfg.item_wrap {
+            let first_is_scalar = list
+                .get_item(0)
+                .ok()
+                .map(|item| is_python_scalar(&item))
+                .unwrap_or(false);
+            let wrap_list_container = (cfg.item_wrap || !first_is_scalar) && !cfg.list_headers;
+
+            if wrap_list_container {
                 write_open_tag(out, &xml_key, name_attr, type_attr(cfg, "list"));
                 write_list_contents(py, out, list, &xml_key, cfg)?;
                 write_close_tag(out, &xml_key);
@@ -354,6 +361,18 @@ fn write_dict_contents(
     Ok(())
 }
 
+/// Return true when a Python object is treated as a primitive scalar by the
+/// pure-Python serializer for list-wrapper decisions.
+#[cfg(feature = "python")]
+#[inline]
+fn is_python_scalar(obj: &Bound<'_, PyAny>) -> bool {
+    obj.is_none()
+        || obj.is_instance_of::<PyBool>()
+        || obj.is_instance_of::<PyInt>()
+        || obj.is_instance_of::<PyFloat>()
+        || obj.is_instance_of::<PyString>()
+}
+
 /// Write all items of a list into the buffer.
 #[cfg(feature = "python")]
 fn write_list_contents(
@@ -363,7 +382,8 @@ fn write_list_contents(
     parent: &str,
     cfg: &ConvertConfig,
 ) -> PyResult<()> {
-    let tag_name = if cfg.list_headers {
+    let scalar_tag_name = if cfg.item_wrap { "item" } else { parent };
+    let dict_tag_name = if cfg.list_headers {
         parent
     } else if cfg.item_wrap {
         "item"
@@ -375,14 +395,19 @@ fn write_list_contents(
         // Dicts inside lists have special wrapping logic
         if let Ok(dict) = item.cast::<PyDict>() {
             if cfg.item_wrap || cfg.list_headers {
-                write_open_tag(out, tag_name, None, type_attr(cfg, "dict"));
+                let dict_type_attr = if cfg.list_headers {
+                    None
+                } else {
+                    type_attr(cfg, "dict")
+                };
+                write_open_tag(out, dict_tag_name, None, dict_type_attr);
                 write_dict_contents(py, out, dict, cfg)?;
-                write_close_tag(out, tag_name);
+                write_close_tag(out, dict_tag_name);
             } else {
                 write_dict_contents(py, out, dict, cfg)?;
             }
         } else {
-            write_value(py, out, &item, tag_name, None, cfg, true)?;
+            write_value(py, out, &item, scalar_tag_name, None, cfg, true)?;
         }
     }
     Ok(())

rust/src/lib.rs

@@ -3,7 +3,7 @@
 
 import json
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, Dict, List
+from typing import TYPE_CHECKING, Any
 
 import pytest
 

tests/conftest.py

@@ -500,6 +500,92 @@ def test_dicttoxml_with_xml_namespaces(self) -> None:
         result = dicttoxml.dicttoxml(data, xml_namespaces=namespaces)
         assert b'xmlns="http://example.com"' in result
 
+    # @lat: [[tests#Conversion behavior#Default xml namespaces stay empty]]
+    def test_dicttoxml_without_xml_namespaces_keeps_previous_output(self) -> None:
+        """Test dicttoxml without xml_namespaces keeps the default XML shape."""
+        data = {"bike": "blue"}
+        result = dicttoxml.dicttoxml(data, attr_type=False)
+        assert (
+            b'<?xml version="1.0" encoding="UTF-8" ?>'
+            b"<root><bike>blue</bike></root>" == result
+        )
+        assert b"xmlns" not in result
+        assert b"xsi:" not in result
+
+    # @lat: [[tests#Conversion behavior#Explicit xml namespaces emit schema attributes]]
+    def test_dicttoxml_with_explicit_xml_namespaces_emits_schema_attributes(self) -> None:
+        """Test dicttoxml emits explicit namespace declarations and XSI schema attributes."""
+        data = {"bike": "blue"}
+        namespaces = {
+            "veh": "https://example.com/vehicle",
+            "xsi": {
+                "schemaInstance": "http://www.w3.org/2001/XMLSchema-instance",
+                "schemaLocation": "https://example.com/vehicle vehicle.xsd",
+                "noNamespaceSchemaLocation": "vehicle-no-namespace.xsd",
+            },
+        }
+        namespaces_before = {
+            prefix: value.copy() if isinstance(value, dict) else value
+            for prefix, value in namespaces.items()
+        }
+
+        result = dicttoxml.dicttoxml(
+            data,
+            custom_root="vehicle",
+            attr_type=False,
+            xml_namespaces=namespaces,
+        )
+
+        assert (
+            b'<?xml version="1.0" encoding="UTF-8" ?>'
+            b'<vehicle xmlns:veh="https://example.com/vehicle" '
+            b'xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" '
+            b'xsi:schemaLocation="https://example.com/vehicle vehicle.xsd">'
+            b"<bike>blue</bike>"
+            b"</vehicle>" == result
+        )
+        assert b"xsi:noNamespaceSchemaLocation" not in result
+        assert namespaces == namespaces_before
+
+    # @lat: [[tests#Conversion behavior#Xml namespace inputs are not mutated across calls]]
+    def test_dicttoxml_reuses_xml_namespaces_without_mutating_input(self) -> None:
+        """Test reusing xml_namespaces across calls does not mutate or accumulate state."""
+        data = {"bike": "blue"}
+        namespaces = {
+            "veh": "https://example.com/vehicle",
+            "xsi": {
+                "schemaInstance": "http://www.w3.org/2001/XMLSchema-instance",
+                "schemaLocation": "https://example.com/vehicle vehicle.xsd",
+            },
+        }
+        namespaces_before = {
+            prefix: value.copy() if isinstance(value, dict) else value
+            for prefix, value in namespaces.items()
+        }
+
+        first = dicttoxml.dicttoxml(
+            data,
+            custom_root="vehicle",
+            attr_type=False,
+            xml_namespaces=namespaces,
+        )
+        second = dicttoxml.dicttoxml(
+            data,
+            custom_root="vehicle",
+            attr_type=False,
+            xml_namespaces=namespaces,
+        )
+
+        assert first == second
+        assert first.count(b'xmlns:veh="https://example.com/vehicle"') == 1
+        assert first.count(
+            b'xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"'
+        ) == 1
+        assert first.count(
+            b'xsi:schemaLocation="https://example.com/vehicle vehicle.xsd"'
+        ) == 1
+        assert namespaces == namespaces_before
+
     def test_datetime_conversion(self) -> None:
         """Test datetime conversion."""
         data = {"key": datetime.datetime(2023, 2, 15, 12, 30, 45)}

tests/test_dict2xml.py

@@ -21,12 +21,6 @@
 class TestJson2xml:
     """Tests for `json2xml` package."""
 
-    def setUp(self) -> None:
-        """Set up test fixtures, if any."""
-
-    def tearDown(self) -> None:
-        """Tear down test fixtures, if any."""
-
     def test_read_from_json(self) -> None:
         """Test something."""
         data = readfromjson("examples/bigexample.json")

tests/test_json2xml.py

@@ -252,7 +252,8 @@ def test_item_wrap_false(self):
     def test_list_headers(self):
         data = {"colors": ["red", "green"]}
         result = rust_dicttoxml(data, list_headers=True)
-        assert b"<colors" in result
+        assert b"<item type=\"str\">red</item>" in result
+        assert b"<item type=\"str\">green</item>" in result
 
 
 class TestRustVsPythonCompatibility:
@@ -334,21 +335,18 @@ def test_item_wrap_false_matches(self):
         rust, python = self.compare_outputs(data, item_wrap=False)
         assert rust == python
 
-    @pytest.mark.xfail(reason="Rust list_headers implementation differs from Python - uses different wrapping semantics")
     def test_list_headers_true_matches(self):
         """Test that list_headers=True produces matching output."""
         data = {"items": ["one", "two", "three"]}
         rust, python = self.compare_outputs(data, list_headers=True)
         assert rust == python
 
-    @pytest.mark.xfail(reason="Rust item_wrap=False with nested dicts differs from Python - known limitation")
     def test_item_wrap_false_with_nested_dict_matches(self):
         """Test item_wrap=False with nested dicts in list."""
         data = {"users": [{"name": "Alice"}, {"name": "Bob"}]}
         rust, python = self.compare_outputs(data, item_wrap=False)
         assert rust == python
 
-    @pytest.mark.xfail(reason="Rust list_headers with nested structures differs from Python - known limitation")
     def test_list_headers_with_nested_matches(self):
         """Test list_headers=True with nested structures."""
         data = {"products": [{"id": 1, "name": "Widget"}, {"id": 2, "name": "Gadget"}]}