Add get_engine and deprecate engine_from_environment (#3151)

#2767 introduced `get_engine_sampler`.  This adds `get_engine` via a similar pattern, and in particular uses the same shared environment variable for projects, GOOGLE_PROJECT_ID.

Also
* deprecates `engine_from_environment` which used a different environment variable and a different nomenclature.  It also fixes a bug in this methods id.
* corrects a typo in the doc of `get_engine_sampler`
* Gives the a sensible small string for an Engine object.

cirq/google/__init__.py

@@ -40,6 +40,7 @@
     EngineTimeSlot,
     ProtoVersion,
     QuantumEngineSampler,
+    get_engine,
     get_engine_sampler,
 )
 

cirq/google/engine/__init__.py

@@ -20,6 +20,7 @@
 
 from cirq.google.engine.engine import (
     Engine,
+    get_engine,
     ProtoVersion,
 )
 

cirq/google/engine/engine.py

@@ -25,6 +25,7 @@
 
 import datetime
 import enum
+import os
 import random
 import string
 from typing import Dict, List, Optional, Sequence, TypeVar, Union, TYPE_CHECKING
@@ -108,7 +109,6 @@ def copy(self) -> 'EngineContext':
     def _value_equality_values_(self):
         return self.proto_version, self.client
 
-
 class Engine:
     """Runs programs via the Quantum Engine API.
 
@@ -133,8 +133,8 @@ def __init__(
             proto_version: Optional[ProtoVersion] = None,
             service_args: Optional[Dict] = None,
             verbose: Optional[bool] = None,
-            context: Optional[EngineContext] = None,
             timeout: Optional[int] = None,
+            context: Optional[EngineContext] = None,
     ) -> None:
         """Supports creating and running programs against the Quantum Engine.
 
@@ -143,7 +143,6 @@ def __init__(
                 API interactions will be attributed to this project and any
                 resources created will be owned by the project. See
                 https://cloud.google.com/resource-manager/docs/creating-managing-projects#identifying_projects
-            context: Engine configuration and context to use.
             proto_version: The version of cirq protos to use. If None, then
                 ProtoVersion.V2 will be used.
             service_args: A dictionary of arguments that can be used to
@@ -152,11 +151,13 @@ def __init__(
                 true.
             timeout: Timeout for polling for results, in seconds.  Default is
                 to never timeout.
+            context: Engine configuration and context to use. For most users
+                this should never be specified.
         """
         if context and (proto_version or service_args or verbose):
             raise ValueError(
-                'either provide context or proto_version, service_args'
-                ' and verbose')
+                'Either provide context or proto_version, service_args'
+                ' and verbose.')
 
         self.project_id = project_id
         if not context:
@@ -166,6 +167,9 @@ def __init__(
                                     timeout=timeout)
         self.context = context
 
+    def __str__(self) -> str:
+        return f'Engine(project_id={self.project_id!r})'
+
     def run(
             self,
             program: 'cirq.Circuit',
@@ -518,3 +522,34 @@ def sampler(self, processor_id: Union[str, List[str]],
         return engine_sampler.QuantumEngineSampler(engine=self,
                                                    processor_id=processor_id,
                                                    gate_set=gate_set)
+
+
+def get_engine(project_id: Optional[str] = None) -> Engine:
+    """Get an Engine instance assuming some sensible defaults.
+
+    This uses the environment variable GOOGLE_CLOUD_PROJECT for the Engine
+    project_id, unless set explicitly. By using an environment variable,
+    you can avoid hard-coding the project_id in shared code.
+
+    If the environment variables are set, but incorrect, an authentication
+    failure will occur when attempting to run jobs on the engine.
+
+    Args:
+        project_id: If set overrides the project id obtained from the
+            environment variable `GOOGLE_CLOUD_PROJECT`.
+
+    Returns:
+        The Engine instance.
+
+    Raises:
+        EnvironmentError: If the environment variable GOOGLE_CLOUD_PROJECT is
+            not set.
+    """
+    env_project_id = 'GOOGLE_CLOUD_PROJECT'
+    if not project_id:
+        project_id = os.environ.get(env_project_id)
+    if not project_id:
+        raise EnvironmentError(
+            f'Environment variable {env_project_id} is not set.')
+
+    return Engine(project_id=project_id)

cirq/google/engine/engine_sampler.py

@@ -11,7 +11,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import os
 from typing import List, TYPE_CHECKING, Union, Optional, cast
 
 from cirq import work, circuits
@@ -72,7 +71,7 @@ def get_engine_sampler(processor_id: str, gate_set_name: str,
         -> 'cirq.google.QuantumEngineSampler':
     """Get an EngineSampler assuming some sensible defaults.
 
-    This uses the environment variable GOOGLE_GLOUD_PROJECT for the Engine
+    This uses the environment variable GOOGLE_CLOUD_PROJECT for the Engine
     project_id, unless set explicitly.
 
     Args:
@@ -84,16 +83,20 @@ def get_engine_sampler(processor_id: str, gate_set_name: str,
             this defaults to the environment variable GOOGLE_CLOUD_PROJECT.
             By using an environment variable, you can avoid hard-coding
             personal project IDs in shared code.
+
+    Returns:
+        A `QuantumEngineSampler` instance.
+
+    Raises:
+         ValueError: If the supplied gate set is not a supported gate set name.
+         EnvironmentError: If no project_id is specified and the environment
+            variable GOOGLE_CLOUD_PROJECT is not set.
     """
     try:
         gate_set = gate_sets.NAMED_GATESETS[gate_set_name]
     except KeyError:
         raise ValueError(f"Please use one of the following gateset names: "
                          f"{sorted(gate_sets.NAMED_GATESETS.keys())}")
 
-    if project_id is None:
-        project_id = os.environ['GOOGLE_CLOUD_PROJECT']
-
-    return engine.Engine(project_id=project_id,
-                         proto_version=engine.ProtoVersion.V2) \
-        .sampler(processor_id=processor_id, gate_set=gate_set)
+    return engine.get_engine(project_id).sampler(processor_id=processor_id,
+                                                 gate_set=gate_set)

cirq/google/engine/engine_test.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 """Tests for engine."""
+import os
 from unittest import mock
 import numpy as np
 import pytest
@@ -258,8 +259,11 @@ def test_create_engine(client):
     with pytest.raises(
             ValueError,
             match='provide context or proto_version, service_args and verbose'):
-        cg.Engine('proj', mock.Mock(), cg.engine.engine.ProtoVersion.V2,
-                  {'args': 'test'}, True)
+        cg.Engine('proj',
+                  proto_version=cg.engine.engine.ProtoVersion.V2,
+                  service_args={'args': 'test'},
+                  verbose=True,
+                  context=mock.Mock())
 
     assert cg.Engine(
         'proj',
@@ -271,6 +275,14 @@ def test_create_engine(client):
     assert client.called_with({'args': 'test'}, True)
 
 
+def test_engine_str():
+    engine = cg.Engine('proj',
+                       proto_version=cg.engine.engine.ProtoVersion.V2,
+                       service_args={'args': 'test'},
+                       verbose=True)
+    assert str(engine) == 'Engine(project_id=\'proj\')'
+
+
 def setup_run_circuit_with_result_(client, result):
     client().create_program.return_value = (
         'prog', qtypes.QuantumProgram(name='projects/proj/programs/prog'))
@@ -692,3 +704,20 @@ def test_sampler(client):
         assert results[i].params.param_dict == {'a': v}
         assert results[i].measurements == {'q': np.array([[0]], dtype='uint8')}
     assert client().create_program.call_args[0][0] == 'proj'
+
+
+@mock.patch('cirq.google.engine.client.quantum.QuantumEngineServiceClient')
+def test_get_engine(build):
+    # Default project id present.
+    with mock.patch.dict(os.environ, {
+            'GOOGLE_CLOUD_PROJECT': 'project!',
+    },
+                         clear=True):
+        eng = cirq.google.get_engine()
+        assert eng.project_id == 'project!'
+
+    # Nothing present.
+    with mock.patch.dict(os.environ, {}, clear=True):
+        with pytest.raises(EnvironmentError, match='GOOGLE_CLOUD_PROJECT'):
+            _ = cirq.google.get_engine()
+        _ = cirq.google.get_engine('project!')

cirq/google/engine/env_config.py

@@ -16,20 +16,27 @@
 
 import os
 
-from cirq.google.engine.engine import Engine
+from typing import TYPE_CHECKING
+
+from cirq.google import engine
+from cirq._compat import deprecated
+
+if TYPE_CHECKING:
+    import cirq
 
 ENV_PROJECT_ID = 'CIRQ_QUANTUM_ENGINE_DEFAULT_PROJECT_ID'
 
 
-def engine_from_environment() -> Engine:
+@deprecated(deadline='v0.10.0', fix='Use cirq.get_engine instead.')
+def engine_from_environment() -> 'cirq.google.Engine':
     """Returns an Engine instance configured using environment variables.
 
     If the environment variables are set, but incorrect, an authentication
     failure will occur when attempting to run jobs on the engine.
 
     Required Environment Variables:
-        QUANTUM_ENGINE_PROJECT: The name of a google cloud project, with the
-            quantum engine enabled, that you have access to.
+        CIRQ_QUANTUM_ENGINE_DEFAULT_PROJECT_ID: The name of a google cloud
+            project, with the quantum engine enabled, that you have access to.
 
     Raises:
         EnvironmentError: The environment variables are not set.
@@ -38,5 +45,4 @@ def engine_from_environment() -> Engine:
     if not project_id:
         raise EnvironmentError(
             'Environment variable {} is not set.'.format(ENV_PROJECT_ID))
-
-    return Engine(project_id=project_id)
+    return engine.get_engine(project_id)

cirq/google/engine/env_config_test.py

@@ -14,23 +14,32 @@
 
 import os
 from unittest import mock
+import warnings
 import pytest
 
 import cirq
 
 
 @mock.patch('cirq.google.engine.client.quantum.QuantumEngineServiceClient')
 def test_engine_from_environment(build):
-    # Default project id present.
-    with mock.patch.dict(os.environ, {
-            'CIRQ_QUANTUM_ENGINE_DEFAULT_PROJECT_ID': 'project!',
-    },
-                         clear=True):
-        eng = cirq.google.engine_from_environment()
-        assert eng.project_id == 'project!'
+    with warnings.catch_warnings():
+        warnings.simplefilter('ignore')
+        # Default project id present.
+        env_dict = {'CIRQ_QUANTUM_ENGINE_DEFAULT_PROJECT_ID': 'project!'}
+        with mock.patch.dict(os.environ, env_dict, clear=True):
+            eng = cirq.google.engine_from_environment()
+            assert eng.project_id == 'project!'
 
-    # Nothing present.
-    with mock.patch.dict(os.environ, {}, clear=True):
-        with pytest.raises(EnvironmentError,
-                           match='CIRQ_QUANTUM_ENGINE_DEFAULT_PROJECT_ID'):
+        # Nothing present.
+        with mock.patch.dict(os.environ, {}, clear=True):
+            with pytest.raises(EnvironmentError,
+                               match='CIRQ_QUANTUM_ENGINE_DEFAULT_PROJECT_ID'):
+                _ = cirq.google.engine_from_environment()
+
+
+def test_deprecation():
+    with cirq.testing.assert_logs('engine_from_environment', 'get_engine',
+                                  'deprecated'):
+        env_dict = {'CIRQ_QUANTUM_ENGINE_DEFAULT_PROJECT_ID': 'project!'}
+        with mock.patch.dict(os.environ, env_dict, clear=True):
             _ = cirq.google.engine_from_environment()

docs/api.rst

@@ -500,7 +500,7 @@ Functionality specific to quantum hardware and services from Google.
     cirq.google.SYC
     cirq.google.SYC_GATESET
     cirq.google.XMON
-    cirq.google.engine_from_environment
+    cirq.google.get_engine
     cirq.google.get_engine_sampler
     cirq.google.is_native_xmon_gate
     cirq.google.is_native_xmon_op
@@ -728,3 +728,4 @@ These objects and methods will be removed in a future version of the library.
     cirq.WaveFunctionSimulatorState
     cirq.WaveFunctionStepResult
     cirq.WaveFunctionTrialResult
+    cirq.google.engine_from_environment