fix

ophyd/signal.py

@@ -44,18 +44,10 @@
 DEFAULT_EPICSSIGNAL_VALUE = UNSET_VALUE
 
 
-class ReadTimeoutError(TimeoutError):
-    ...
+class ReadTimeoutError(TimeoutError): ...
 
 
-class ConnectionTimeoutError(TimeoutError):
-    ...
-
-
-class UndeterminedDataType(Exception):
-    def __init__(self, dtype=None, shape=None):
-        self.dtype = np.dtype(dtype).name if dtype is not None else ""
-        self.shape = shape
+class ConnectionTimeoutError(TimeoutError): ...
 
 
 class Signal(OphydObject):
@@ -104,7 +96,7 @@ def __init__(
         self,
         *,
         name,
-        value=UNSET_VALUE,
+        value=0.0,
         dtype=None,
         shape=None,
         timestamp=None,
@@ -128,37 +120,48 @@ def __init__(
         self._dispatcher = cl.get_dispatcher()
         self._metadata_thread_ctx = self._dispatcher.get_thread_context("monitor")
 
-        # try to apply good default, if possible
-        try:
-            if dtype is None:
-                if value is UNSET_VALUE:
-                    if shape is None:
-                        value = 0.0
-                        raise UndeterminedDataType()
-                    else:
-                        raise UndeterminedDataType(shape=shape)
+        self._value_dtype_str = (
+            "" if dtype in (None, "string") else np.dtype(dtype).name
+        )
+        self._value_shape = shape if not dtype == "string" else ()
+        # check if value corresponds to specified info (or if it is compatible)
+        if dtype not in (None, "string") and value is not UNSET_VALUE:
+            value_array = np.asanyarray(value)
+
+            try:
+                value_array.astype(dtype, casting="same_kind")
+            except TypeError:
+                dtype_ok = False
+                # check if conversion between signed int to unsigned int would be fine
+                if value_array.dtype.kind == "i" and np.dtype(dtype).kind == "u":
+                    bounds = np.iinfo(dtype)
+                    if np.all(value_array >= bounds.min) and np.all(
+                        value_array <= bounds.max
+                    ):
+                        dtype_ok = True
+            else:
+                dtype_ok = True
+
+            if not dtype_ok:
+                if np.isscalar(value) and value == 0.0:
+                    # default is not ok, change to UNSET_VALUE
+                    # (value will be read via .get() - it does not mean it will correspond
+                    # to the desired dtype, though...)
+                    value = UNSET_VALUE
                 else:
-                    try:
-                        inferred_type = data_type(value)
-                    except ValueError:
-                        raise UndeterminedDataType()
-                    else:
-                        if inferred_type == "integer":
-                            dtype = int
-                        elif inferred_type == "number":
-                            dtype = float
-                        else:
-                            raise UndeterminedDataType()
-                        if shape is None:
-                            shape = data_shape(value)
-        except UndeterminedDataType as exc:
-            self._value_dtype_str = exc.dtype
-            self._value_shape = exc.shape
-            self._readback = value
+                    raise TypeError(
+                        f"The value {value} does not match the required dtype {dtype}."
+                    )
         else:
-            self._value_dtype_str = "" if dtype == "string" else np.dtype(dtype).name
-            self._value_shape = () if shape is None else shape
-            self._readback = value
+            if dtype == "string" and np.isscalar(value) and value == 0.0:
+                value = UNSET_VALUE
+        if shape is not None and value is not UNSET_VALUE:
+            if np.asanyarray(value).shape != shape:
+                raise TypeError(
+                    f"The value {value} does not have the required shape {shape}."
+                )
+
+        self._readback = value
 
         if timestamp is None:
             timestamp = time.time()
@@ -1018,6 +1021,8 @@ def __init__(
 
         if string:
             kwargs["dtype"] = "string"
+        kwargs.setdefault("value", UNSET_VALUE)  # no default
+
         super().__init__(name=name, metadata=metadata, **kwargs)
 
         validate_pv_name(read_pv)

ophyd/tests/test_signal.py

@@ -721,7 +721,7 @@ def test_signal_dtype_shape_info(fake_motor_ioc, cleanup):
     original = Signal(name="original", value=1)
     original_desc = original.describe()["original"]
     assert original_desc["dtype"] == "integer"
-    assert original_desc["dtype_numpy"] == "int64"
+    assert original_desc["dtype_numpy"] == ""
     assert original_desc["shape"] == []
     assert original.get() == 1
     original = Signal(name="original", value="On")