Enable more memory regions on the QVM (#873)

CHANGELOG.md

@@ -24,6 +24,10 @@ Changelog
     readout symmetrization (@joshcombes, gh-919).
 -   The ProtoQuil restrictions built in to PyQVM have been removed
     (@ecpeterson, gh-874).
+-   Add the ability to query for other memory regions after both QPU and QVM
+    runs. This removes a previously unnecessary restriction on the QVM, although
+    `ro` remains the only QPU-writeable memory region during Quil execution
+    (@ecpeterson, gh-873).
 
 ### Bugfixes
 

pyquil/api/_qam.py

@@ -16,6 +16,7 @@
 import warnings
 
 from abc import ABC, abstractmethod
+from collections import defaultdict
 
 from rpcq.messages import ParameterAref
 
@@ -54,7 +55,7 @@ def load(self, executable):
 
         self._variables_shim = {}
         self._executable = executable
-        self._bitstrings = None
+        self._memory_results = defaultdict(lambda: None)
         self.status = 'loaded'
         return self
 
@@ -104,12 +105,8 @@ def read_memory(self, *, region_name: str):
         :return: A list of values of the appropriate type.
         """
         assert self.status == 'done'
-        if region_name != "ro":
-            raise QAMError("Currently only allowed to read measurement data from ro.")
-        if self._bitstrings is None:
-            raise QAMError("Bitstrings have not yet been populated. Something has gone wrong.")
 
-        return self._bitstrings
+        return self._memory_results[region_name]
 
     @_record_call
     def read_from_memory_region(self, *, region_name: str):
@@ -125,13 +122,8 @@ def read_from_memory_region(self, *, region_name: str):
         warnings.warn("pyquil.api._qam.QAM.read_from_memory_region is deprecated, please use "
                       "pyquil.api._qam.QAM.read_memory instead.",
                       DeprecationWarning)
-        assert self.status == 'done'
-        if region_name != "ro":
-            raise QAMError("Currently only allowed to read measurement data from ro.")
-        if self._bitstrings is None:
-            raise QAMError("Bitstrings have not yet been populated. Something has gone wrong.")
 
-        return self._bitstrings
+        return self.read_memory(region_name=region_name)
 
     @_record_call
     def reset(self):
@@ -142,6 +134,6 @@ def reset(self):
         """
         self._variables_shim = {}
         self._executable = None
-        self._bitstrings = None
+        self._memory_results = defaultdict(lambda: None)
 
         self.status = 'connected'

pyquil/api/_qpu.py

@@ -13,6 +13,7 @@
 #    See the License for the specific language governing permissions and
 #    limitations under the License.
 ##############################################################################
+from collections import defaultdict
 import uuid
 import warnings
 from typing import Dict, List, Optional, Tuple, Union
@@ -168,8 +169,12 @@ def run(self, run_priority: Optional[int] = None):
         else:
             bitstrings = None
 
-        self._bitstrings = bitstrings
+        self._memory_results = defaultdict(lambda: None)
+        for aref, vals in self._variables_shim.items():
+            self._memory_results[aref] = [vals] * ro_sources[0].shape[0]
+        self._memory_results["ro"] = bitstrings
         self._last_results = results
+
         return self
 
     def _get_buffers(self, job_id: str) -> Dict[str, np.ndarray]:

pyquil/api/_qvm.py

@@ -510,18 +510,16 @@ def run(self):
             quil_program = apply_noise_model(quil_program, self.noise_model)
 
         quil_program = self.augment_program_with_memory_values(quil_program)
-        try:
-            self._bitstrings = self.connection._qvm_run(quil_program=quil_program,
+
+        self._memory_results = self.connection._qvm_run(quil_program=quil_program,
                                                         classical_addresses=classical_addresses,
                                                         trials=trials,
                                                         measurement_noise=self.measurement_noise,
                                                         gate_noise=self.gate_noise,
-                                                        random_seed=self.random_seed)['ro']
-        except KeyError:
-            warnings.warn("You are running a QVM program with no MEASURE instructions. "
-                          "The result of this program will always be an empty array. Are "
-                          "you sure you didn't mean to measure some of your qubits?")
-            self._bitstrings = np.zeros((trials, 0), dtype=np.int64)
+                                                        random_seed=self.random_seed)
+
+        if "ro" not in self._memory_results or self._memory_results["ro"] == []:
+            self._memory_results["ro"] = np.zeros((trials, 0), dtype=np.int64)
 
         return self
 

pyquil/pyqvm.py

@@ -186,7 +186,7 @@ def __init__(self, n_qubits, quantum_simulator_type: Type[AbstractQuantumSimulat
         # private implementation details
         self._qubit_to_ram = None  # type: Dict[int, int]
         self._ro_size = None  # type :int
-        self._bitstrings = None  # type: np.ndarray
+        self._memory_results = None  # type: Dict[str, np.ndarray]
 
         self.rs = np.random.RandomState(seed=seed)
         self.wf_simulator = quantum_simulator_type(n_qubits=n_qubits, rs=self.rs)
@@ -201,7 +201,7 @@ def load(self, executable):
         # initialize program counter
         self.program = program
         self.program_counter = 0
-        self._bitstrings = None
+        self._memory_results = None
 
         # clear RAM, although it's not strictly clear if this should happen here
         self.ram = {}

pyquil/tests/test_quantum_computer.py

@@ -536,15 +536,15 @@ def test_reset(forest):
     aref = ParameterAref(name='theta', index=0)
     assert qc.qam._variables_shim[aref] == np.pi
     assert qc.qam._executable == p
-    assert qc.qam._bitstrings.shape == (1000, 1)
-    assert all([bit == 1 for bit in qc.qam._bitstrings])
+    assert qc.qam._memory_results["ro"].shape == (1000, 1)
+    assert all([bit == 1 for bit in qc.qam._memory_results["ro"]])
     assert qc.qam.status == 'done'
 
     qc.reset()
 
     assert qc.qam._variables_shim == {}
     assert qc.qam._executable is None
-    assert qc.qam._bitstrings is None
+    assert qc.qam._memory_results["ro"] is None
     assert qc.qam.status == 'connected'