Structs: remove '_from_values', create '_push_to' method

src/extrainterpreters/utils.py

@@ -144,14 +144,6 @@ def _fields(cls):
             if isinstance(v, RawField):
                 yield k
 
-    @classmethod
-    def _from_values(cls, *args):
-        data = bytearray(b"\x00" * cls._size)
-        self = cls(data, 0)
-        for arg, field_name in zip(args, self._fields):
-            setattr(self, field_name, arg)
-        return self
-
     @property
     def _bytes(self):
         return bytes(self._data[self._offset : self._offset + self._size])
@@ -173,6 +165,14 @@ def _get_offset_for_field(cls, field_name):
         field = getattr(cls, field_name)
         return field._calc_offset(cls)
 
+    def _push_to(self, data, offset=0):
+        """Paste struct data into a new buffer given by data, offset
+
+        Returns a new instance pointing to the data in the new copy.
+        """
+        data[offset: offset + self._size] = self._bytes
+        return self._from_data(data, offset)
+
     def __repr__(self):
         field_data = []
         for field_name in self._fields:

tests/test_struct.py

@@ -65,6 +65,18 @@ class Struct(StructBase):
     assert s.data_offset == 1000
     assert s.length == 2_000_000
 
+def test_struct_push_to():
+    class Struct(StructBase):
+        data_offset = Field(2)
+        length = Field(4)
+
+    s = Struct(data_offset=1000, length=2_000_000)
+
+    data = bytearray(Struct._size)
+    n = s._push_to(data, 0)
+    assert n.data_offset == 1000
+    assert n.length == 2_000_000
+
 
 def test_struct_bytes():
     class Struct(StructBase):