Implement _fields and _asdict() for struct.

capnpy/compiler/struct_.py

@@ -65,6 +65,7 @@ def emit_definition(self, m):
                 __static_ptrs_size__ = {ptrs_size}
 
             """)
+            self._emit_fields(m, ns)
             for child in m.children[self.id]:
                 child.emit_reference_as_child(m)
             m.w()
@@ -97,6 +98,12 @@ def _get_enum_items(self, m):
                 enum_items[field.discriminantValue] = m._field_name(field)
         return enum_items
 
+    def _emit_fields(self, m, ns):
+        fnames = []
+        for f in self.struct.fields or []:
+            fnames.append(m._field_name(f))
+        ns.w("_fields = {}".format(tuple(fnames)))
+
     def _emit_union_tag_declaration(self, m):
         enum_items = self._get_enum_items(m)
         if not enum_items:

capnpy/struct_.py

@@ -1,3 +1,5 @@
+from collections import OrderedDict
+
 import capnpy
 from capnpy import ptr
 from capnpy.type import Types
@@ -44,6 +46,8 @@ class Struct(Blob):
     __static_data_size__ = None
     __static_ptrs_size__ = None
 
+    _fields = None
+
     def __init__(self, buf, offset, data_size, ptrs_size):
         self._init_from_buffer(buf, offset, data_size, ptrs_size)
 
@@ -69,6 +73,12 @@ def __reduce__(self):
                 self._data_size, self._ptrs_size)
         return (struct_from_buffer, args)
 
+    def _asdict(self):
+        o = OrderedDict()
+        for f in self._fields:
+            o[f] = getattr(self, f)
+        return o
+
     @classmethod
     def from_buffer(cls, buf, offset, data_size, ptrs_size):
         return struct_from_buffer(cls, buf, offset, data_size, ptrs_size)

capnpy/testing/compiler/test_todict.py

@@ -0,0 +1,29 @@
+from capnpy.testing.compiler.support import CompilerTest
+
+
+class TestTodict(CompilerTest):
+    def test_fields(self):
+        schema = """
+        @0xbf5147cbbecf40c1;
+        struct Point {
+            x @0 :Int64;
+            y @1 :Int64;
+        }
+        """
+        mod = self.compile(schema)
+        assert mod.Point._fields == ('x', 'y')
+
+    def test_todict(self):
+        schema = """
+        @0xbf5147cbbecf40c1;
+        struct Point {
+            x @0 :Int64;
+            y @1 :Int64;
+        }
+        """
+        mod = self.compile(schema)
+        p = mod.Point(1, 2)
+        d = p._asdict()
+        assert d == {'x': 1, 'y': 2}
+        assert list(d)[0] == 'x'
+

docs/source/usage.rst

@@ -266,6 +266,9 @@ inspired by ``namedtuples``:
     value of a field, you can instantiate a new object, as you would do with
     namedtuples
 
+  - ``_fields`` and ``_asdict()`` are provided with the same semantics as
+    namedtuple
+
   - objects can be made `comparable and hashable`__ by specifying the
     ``$Py.key`` annotation