Fix for empty array

pyaml/arrays/bpm_array.py

@@ -77,7 +77,7 @@ def __init__(self, arrayName: str, bpms: list[BPM], use_aggregator=True):
         self.__hpos = RWBPMSinglePosition(arrayName, bpms, 0)
         self.__vpos = RWBPMSinglePosition(arrayName, bpms, 1)
 
-        if use_aggregator:
+        if use_aggregator and len(bpms) > 0:
             aggs = self.get_peer().create_bpm_aggregators(bpms)
             self.__hvpos.set_aggregator(aggs[0])
             self.__hpos.set_aggregator(aggs[1])

pyaml/arrays/element_array.py

@@ -30,14 +30,15 @@ def __init__(self, arrayName: str, elements: list[Element], use_aggregator=True)
         """
         super().__init__(i for i in elements)
         self.__name = arrayName
-        self.__peer = self[0]._peer if len(self) > 0 else None
-        self.__use_aggretator = use_aggregator
-        if self.__peer is None or any([m._peer != self.__peer for m in self]):
-            raise PyAMLException(
-                f"{self.__class__.__name__} {self.get_name()}: "
-                "All elements must be attached to the same instance "
-                "of either a Simulator or a ControlSystem"
-            )
+        if len(elements) > 0:
+            self.__peer = self[0]._peer if len(self) > 0 else None
+            self.__use_aggretator = use_aggregator
+            if self.__peer is None or any([m._peer != self.__peer for m in self]):
+                raise PyAMLException(
+                    f"{self.__class__.__name__} {self.get_name()}: "
+                    "All elements must be attached to the same instance "
+                    "of either a Simulator or a ControlSystem"
+                )
 
     def get_peer(self):
         """

pyaml/arrays/magnet_array.py

@@ -103,7 +103,7 @@ def __init__(self, arrayName: str, magnets: list[Magnet], use_aggregator=True):
         self.__rwstrengths = RWMagnetStrength(arrayName, magnets)
         self.__rwhardwares = RWMagnetHardware(arrayName, magnets)
 
-        if use_aggregator:
+        if use_aggregator and len(magnets) > 0:
             aggs = self.get_peer().create_magnet_strength_aggregator(magnets)
             aggh = self.get_peer().create_magnet_harddware_aggregator(magnets)
             self.__rwstrengths.set_aggregator(aggs)

tests/test_arrays.py

@@ -4,9 +4,15 @@
 import pytest
 
 from pyaml.accelerator import Accelerator
+from pyaml.arrays.bpm import BPM
+from pyaml.arrays.bpm import ConfigModel as BPMArrayConfigModel
 from pyaml.arrays.bpm_array import BPMArray
+from pyaml.arrays.cfm_magnet import CombinedFunctionMagnet
+from pyaml.arrays.cfm_magnet import ConfigModel as CombinedFunctionMagnetConfigModel
 from pyaml.arrays.cfm_magnet_array import CombinedFunctionMagnetArray
 from pyaml.arrays.element_array import ElementArray
+from pyaml.arrays.magnet import ConfigModel as MagnetArrayConfigModel
+from pyaml.arrays.magnet import Magnet
 from pyaml.arrays.magnet_array import MagnetArray
 from pyaml.configuration.factory import Factory
 
@@ -220,4 +226,22 @@ def test_arrays(install_test_package):
     magSH1AC = acfm["model_name:SH1A-*"]  # All SH1A magnets (CFMs only)
     assert isinstance(magSH1AC, ElementArray) and len(magSH1AC) == 32
 
+    # Empty arrays
+    emptyMag = Magnet(MagnetArrayConfigModel(name="EmptyMag", elements=[]))
+    emptyMag.fill_array(sr.design)  # Attach the array
+    v = sr.design.get_magnets("EmptyMag").strengths.get()  # Ensure good attach
+    assert np.shape(v) == (0,)
+
+    emptyBPM = BPM(BPMArrayConfigModel(name="emptyBPM", elements=[]))
+    emptyBPM.fill_array(sr.design)  # Attach the array
+    v = sr.design.get_bpms("emptyBPM").positions.get()  # Ensure good attach
+    assert np.shape(v) == (0,)
+
+    emptyCFM = CombinedFunctionMagnet(
+        CombinedFunctionMagnetConfigModel(name="emptyCFM", elements=[])
+    )
+    emptyCFM.fill_array(sr.design)  # Attach the array
+    v = sr.design.get_cfm_magnets("emptyCFM").strengths.get()  # Ensure good attach
+    assert np.shape(v) == (0,)
+
     Factory.clear()