Add plugin interface for external provider registration

qiskit/backends/providers.py

@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2018, IBM.
+#
+# This source code is licensed under the Apache License, Version 2.0 found in
+# the LICENSE.txt file in the root directory of this source tree.
+
+"""Provider plugin manager."""
+
+import logging
+
+import stevedore
+
+logger = logging.getLogger(__name__)
+
+
+class ProviderPluginManager:
+    """Qiskit provider plugin manager class
+
+    This class is used to manage the lifecycle of external backend provider
+    plugins. It provides functions for getting all backends
+    """
+    def __init__(self):
+        self.ext_plugins = stevedore.ExtensionManager(
+            'qiskit.providers', invoke_on_load=True,
+            propagate_map_exceptions=True,
+            on_load_failure_callback=self.failure_hook)
+
+    @staticmethod
+    def failure_hook(_, err_plugin, err):
+        """Log errors on import and don't fail."""
+        logger.error("Could not load provider plugin %r with error: %s",
+                     err_plugin.name, err)
+
+    def get_providers(self):
+        """Return dict of all discovered provider plugins."""
+        providers = {}
+        for plug in self.ext_plugins:
+            providers[plug.name] = plug.obj
+        return providers
+
+    def get_all_backends(self):
+        """Return dict of lists of backends for all discovered provider plugins."""
+        backends_dict = {}
+        for plug in self.ext_plugins:
+            backends_dict[plug.name] = plug.obj.backends()
+        return backends_dict

qiskit/providers/__init__.py

@@ -9,12 +9,17 @@
 
 import pkgutil
 
+from qiskit.backends.providers import ProviderPluginManager
 from .basebackend import BaseBackend
 from .baseprovider import BaseProvider
 from .basejob import BaseJob
 from .exceptions import JobError, JobTimeoutError, QiskitBackendNotFoundError
 from .jobstatus import JobStatus
 
 
+ALL_PROVIDERS = ProviderPluginManager().get_providers()
+for prov in ALL_PROVIDERS:
+    globals()[prov] = ALL_PROVIDERS[prov]
+
 # Allow extending this namespace.
 __path__ = pkgutil.extend_path(__path__, __name__)

requirements.txt

@@ -8,3 +8,4 @@ ply>=3.10
 psutil>=5
 scipy>=0.19
 sympy>=1.3
+stevedore>=1.30.0

setup.py

@@ -24,6 +24,7 @@
     "psutil>=5",
     "scipy>=0.19,!=0.19.1",
     "sympy>=1.3"
+    "stevedore>=1.30.0"
 ]
 
 # Add Cython extensions here