New Format.__deltiem__ and expanding __setitem__.

bitformat/_format.py

@@ -300,7 +300,7 @@ def __getitem__(self, key: slice | str | int) -> Any:
         except KeyError:
             raise KeyError(f"Field with name '{key}' not found.")
 
-    def __setitem__(self, name: str, value: str | FieldType) -> None:
+    def __setitem__(self, key: slice | str | int, value: str | FieldType) -> None:
         if isinstance(value, str):
             try:
                 field = FieldType.from_string(value)
@@ -310,11 +310,33 @@ def __setitem__(self, name: str, value: str | FieldType) -> None:
             field = value
         else:
             raise ValueError(f"Can't create and set field from type '{type(value)}'.")
-        for i in range(len(self._fields)):
-            if self._fields[i].name == name:
-                self._fields[i] = field
-                return
-        raise KeyError(f"Field with name '{name}' not found.")
+        if isinstance(key, int):
+            self._fields[key] = field
+        elif isinstance(key, slice):
+            self._fields[key] = field
+        elif isinstance(key, str):
+            for i in range(len(self._fields)):
+                if self._fields[i].name == key:
+                    self._fields[i] = field
+                    return
+            raise KeyError(f"Field with name '{key}' not found.")
+        else:
+            raise TypeError(f"Invalid key type {type(key)}.")
+
+    def __delitem__(self, key: slice | int | str):
+        if isinstance(key, int):
+            del self._fields[key]
+        elif isinstance(key, slice):
+            del self._fields[key]
+        elif isinstance(key, str):
+            for i in range(len(self._fields)):
+                # TODO: Can we use _field_names here?
+                if self._fields[i].name == key:
+                    del self._fields[i]
+                    return
+            raise KeyError(f"Field with name '{key}' not found.")
+        else:
+            raise TypeError(f"Invalid key type {type(key)}.")
 
     @override
     def _str(self, indent: Indenter) -> str:

tests/test_format.py

@@ -644,3 +644,39 @@ def test_wrong_arguments():
     with pytest.raises(TypeError):
         f.pack(1)
     f.pack([1])
+
+def test_slicing_fields():
+    f = Format.from_string("x = (u8, u7, u6, u5, u4, u3, u2, u1)")
+    f.pack([8, 7, 6, 5, 4, 3, 2, 1])
+    assert f[0].value == 8
+    assert f[-1].value == 1
+    assert f[:2].value == [8, 7]
+    assert f[2::-1].value == [6, 7, 8]
+    assert f[::2].value == [8, 6, 4, 2]
+    f2 = f[::2]
+    assert f2[1].dtype == Dtype("u6")
+    assert f2[1].value == 6
+    f2[1].value = 7
+    assert f2[1].value == 7
+    assert f[2].value == 6
+    with pytest.raises(IndexError):
+        _ = f[8]
+    for field in f:
+        assert field.value == field.dtype.bit_length
+
+def test_deleting_fields():
+    f = Format.from_params(["x: u8", "y: u8", "z: u8"])
+    del f[1]
+    assert len(f) == 2
+    assert f[1].name == "z"
+
+def test_setting_fields():
+    f = Format.from_params(["x: u8", "y: u8", "z: u8", "q:i4"])
+    g = Format.from_params(["a: u8", "b: u8", "c: u8"])
+    f[2] = Field("u15 = 5")
+    assert f[2].value == 5
+    f[0:2] = g[:]
+    assert f[0].name == "a"
+    assert len(f) == 5
+
+