Minimal change to allow support of HID descriptors

usb_protocol/emitters/descriptors/standard.py

@@ -208,12 +208,14 @@ class DeviceDescriptorCollection:
         return index
 
 
-    def add_descriptor(self, descriptor, index=0):
+    def add_descriptor(self, descriptor, index=0, descriptor_type=None):
         """ Adds a descriptor to our collection.
 
         Parameters:
-            descriptor -- The descriptor to be added.
-            index      -- The index of the relevant descriptor. Defaults to 0.
+            descriptor      -- The descriptor to be added.
+            index           -- The index of the relevant descriptor. Defaults to 0.
+            descriptor_type -- The type of the descriptor to be added. If `None`,
+                               this is automatically derived from the descriptor contents.
         """
 
         # If this is an emitter rather than a descriptor itself, convert it.
@@ -221,7 +223,8 @@ class DeviceDescriptorCollection:
             descriptor = descriptor.emit()
 
         # Figure out the identifier (type + index) for this descriptor...
-        descriptor_type = descriptor[1]
+        if (descriptor_type is None):
+            descriptor_type = descriptor[1]
         identifier = descriptor_type, index
 
         # ... and store it.
@@ -566,5 +569,3 @@ class EmitterTests(unittest.TestCase):
 
 if __name__ == "__main__":
     unittest.main()
-
-