Use the un-underscored name if no alias attribute is there. (#416)

* Simplify code as cattrs depends on modern attrs

This modern version of `attrs` provides the `alias` attribute on
fields that contains the name we should use here.

Also add a test to verify that structuring and unstructuring aliased
attributes (which can be triggered by prefixing an attribute with an
underscore) works as expected.

* Tweak test

---------

Co-authored-by: Tin Tvrtković <[email protected]>

Author: jap

HISTORY.md

@@ -45,6 +45,8 @@
   ([#420](https://github.com/python-attrs/cattrs/pull/420))
 - Add support for `datetime.date`s to the PyYAML preconfigured converter.
   ([#393](https://github.com/python-attrs/cattrs/issues/393))
+- Remove some unused lines in the unstructuring code.
+  ([#416](https://github.com/python-attrs/cattrs/pull/416))
 
 ## 23.1.2 (2023-06-02)
 

src/cattrs/converters.py

@@ -509,16 +509,12 @@ def structure_attrs_fromdict(self, obj: Mapping[str, Any], cl: Type[T]) -> T:
 
         conv_obj = {}  # Start with a fresh dict, to ignore extra keys.
         for a in fields(cl):
-            name = a.name
-
             try:
-                val = obj[name]
+                val = obj[a.name]
             except KeyError:
                 continue
 
-            if name[0] == "_":
-                name = name[1:]
-
+            # try .alias and .name because this code also supports dataclasses!
             conv_obj[getattr(a, "alias", a.name)] = self._structure_attribute(a, val)
 
         return cl(**conv_obj)

tests/test_converter.py

@@ -17,7 +17,7 @@
 from hypothesis import HealthCheck, assume, given, settings
 from hypothesis.strategies import booleans, just, lists, one_of, sampled_from
 
-from cattrs import Converter, UnstructureStrategy
+from cattrs import BaseConverter, Converter, UnstructureStrategy
 from cattrs.errors import ClassValidationError, ForbiddenExtraKeysError
 from cattrs.gen import make_dict_structure_fn, override
 
@@ -381,6 +381,23 @@ class C:
     assert inst == converter.structure(unstructured, C)
 
 
+def test_dict_roundtrip_with_alias():
+    """
+    A class with an aliased attribute can be unstructured and structured.
+    """
+
+    converter = BaseConverter()
+
+    @define
+    class C:
+        _a: int
+
+    inst = C(a=0)
+    unstructured = converter.unstructure(inst)
+    assert unstructured == {"_a": 0}
+    assert converter.structure(unstructured, C) == inst
+
+
 @given(simple_typed_classes(defaults=True))
 def test_type_overrides(cl_and_vals):
     """