Fix comment. Fix the force option. Add docstring.

theano/gpuarray/__init__.py

@@ -114,15 +114,39 @@ init_dev.devmap = {}
 def use(device,
         force=False,
         default_to_move_computation_to_gpu=True,
-        move_shared_float32_to_gpu=True):
+        move_shared_to_gpu=True):
+    """
+    Error and warning about CUDA should be displayed only when this
+    function is called. We need to be able to load this module only
+    to check if it is available!
+
+    Parameters
+    ----------
+    device : string
+        "cuda", "cuda0", "cudaN", "" (N is the device number to use).
+        "" mean do all the rest and don't init a device.
+    force
+        Will always raise an exception if we can't use the gpu.
+    default_to_move_computation_to_gpu
+        If gpu init succeeded, enable by default optimizations to move
+        computations to the gpu.
+    move_shared_to_gpu
+        If gpu init succeeded, put new shared variables on the gpu.
+
+    """
+    if force:
+        if not device.startswith('cuda'):
+            raise Exception("forced the init and bad device provided: " +
+                            device)
+        else:
+            # If we force, the device should not already be initialized.
+            assert device not in init_dev.devmap
     if device:
         init_dev(device)
-    elif forece:
-        raise Exception("No device provided")
     if default_to_move_computation_to_gpu:
         optdb.add_tags('gpuarray_opt', 'fast_run', 'fast_compile')
         optdb.add_tags('gpua_scanOp_make_inplace', 'fast_run')
-    if move_shared_float32_to_gpu:
+    if move_shared_to_gpu:
         import theano.compile
         theano.compile.shared_constructor(gpuarray_shared_constructor)