Add AbstractEngine objects to cirq_google.engine __init__ (#4759)

* Add AbstractEngine objects to cirq_google.engine __init__

cirq-google/cirq_google/engine/__init__.py

@@ -15,6 +15,53 @@
 """Client for running on Google's Quantum Engine.
 """
 
+from cirq_google.engine.abstract_engine import (
+    AbstractEngine,
+)
+
+from cirq_google.engine.abstract_job import (
+    AbstractJob,
+)
+
+from cirq_google.engine.abstract_processor import (
+    AbstractProcessor,
+)
+
+from cirq_google.engine.abstract_program import (
+    AbstractProgram,
+)
+
+from cirq_google.engine.abstract_local_engine import (
+    AbstractLocalEngine,
+)
+
+from cirq_google.engine.abstract_local_job import (
+    AbstractLocalJob,
+)
+
+from cirq_google.engine.abstract_local_processor import (
+    AbstractLocalProcessor,
+)
+
+from cirq_google.engine.abstract_local_program import (
+    AbstractLocalProgram,
+)
+
+from cirq_google.engine.simulated_local_engine import (
+    SimulatedLocalEngine,
+)
+
+from cirq_google.engine.simulated_local_job import (
+    SimulatedLocalJob,
+)
+
+from cirq_google.engine.simulated_local_processor import (
+    SimulatedLocalProcessor,
+)
+
+from cirq_google.engine.simulated_local_program import (
+    SimulatedLocalProgram,
+)
 from cirq_google.engine.calibration import (
     Calibration,
 )

cirq-google/cirq_google/engine/simulated_local_processor.py

@@ -18,16 +18,14 @@
 import cirq
 
 from cirq_google.api import v2
-from cirq_google.engine import calibration
+from cirq_google.engine import calibration, validating_sampler
 from cirq_google.engine.abstract_local_processor import AbstractLocalProcessor
 from cirq_google.engine.abstract_local_program import AbstractLocalProgram
 from cirq_google.engine.abstract_program import AbstractProgram
 from cirq_google.engine.local_simulation_type import LocalSimulationType
 from cirq_google.engine.simulated_local_job import SimulatedLocalJob
 from cirq_google.engine.simulated_local_program import SimulatedLocalProgram
 
-import cirq_google.engine.validating_sampler as validating_sampler
-
 if TYPE_CHECKING:
     from cirq_google.serialization.serializer import Serializer
 

cirq-google/cirq_google/experimental/noise_models/noise_models.py

@@ -13,11 +13,13 @@
 # limitations under the License.
 
 from math import exp
-from typing import Dict, Sequence
+from typing import Dict, Sequence, TYPE_CHECKING
 
 import cirq
 from cirq.devices.noise_model import validate_all_measurements
-from cirq_google import engine
+
+if TYPE_CHECKING:
+    from cirq_google.engine import calibration
 
 
 class PerQubitDepolarizingWithDampedReadoutNoiseModel(cirq.NoiseModel):
@@ -94,7 +96,7 @@ def noisy_moment(self, moment: cirq.Moment, system_qubits: Sequence[cirq.Qid]) -
 
 
 def simple_noise_from_calibration_metrics(
-    calibration: engine.Calibration,
+    calibration: 'calibration.Calibration',
     depol_noise: bool = False,
     damping_noise: bool = False,
     readout_decay_noise: bool = False,