add bullet_client.py to pybullet_utils, with simple example

examples/pybullet/gym/pybullet_utils/bullet_client.py

@@ -0,0 +1,50 @@
+"""A wrapper for pybullet to manage different clients."""
+from __future__ import absolute_import
+from __future__ import division
+import functools
+import inspect
+import pybullet
+
+
+class BulletClient(object):
+  """A wrapper for pybullet to manage different clients."""
+
+  def __init__(self, connection_mode=None):
+    """Creates a Bullet client and connects to a simulation.
+
+    Args:
+      connection_mode:
+        `None` connects to an existing simulation or, if fails, creates a
+          new headless simulation,
+        `pybullet.GUI` creates a new simulation with a GUI,
+        `pybullet.DIRECT` creates a headless simulation,
+        `pybullet.SHARED_MEMORY` connects to an existing simulation.
+    """
+    self._shapes = {}
+
+    if connection_mode is None:
+      self._client = pybullet.connect(pybullet.SHARED_MEMORY)
+      if self._client >= 0:
+        return
+      else:
+        connection_mode = pybullet.DIRECT
+    self._client = pybullet.connect(connection_mode)
+
+  def __del__(self):
+    """Clean up connection if not already done."""
+    try:
+      pybullet.disconnect(physicsClientId=self._client)
+    except pybullet.error:
+      pass
+
+  def __getattr__(self, name):
+    """Inject the client id into Bullet functions."""
+    attribute = getattr(pybullet, name)
+    if inspect.isbuiltin(attribute):
+      if name not in [
+          "invertTransform", "multiplyTransforms", "getMatrixFromQuaternion",
+          "getEulerFromQuaternion", "computeViewMatrixFromYawPitchRoll",
+          "computeProjectionMatrixFOV", "getQuaternionFromEuler",
+      ]:  # A temporary hack for now.
+        attribute = functools.partial(attribute, physicsClientId=self._client)
+    return attribute