[docs] convertDoxygen.py: remove old __DOC.py files before running

...otherwise, the old generated python docstrings will cause new docstring
generation to be skipped... but the new docstrings are still written out
as empty

The result was that, before this change, every other run of docstring
generation would wipe most of the docstrings

docs/python/convertDoxygen.py

@@ -60,6 +60,32 @@
 if not (xml_file or xml_index_file) or not output_file or GetArg(['--help', '-h']):
     Usage()
 
+packageName = GetArgValue(['--package', '-p'])
+modules = GetArgValue(['--module', '-m'])
+if not packageName:
+    Error("Required option --package not specified")
+if not modules:
+    Error("Required option --module not specified")
+
+
+module_list = [x for x in modules.split(",") if x]
+output_files = []
+for moduleName in module_list:
+    if len(module_list) == 1 and output_file.endswith(".py"):
+        module_output_file = output_file
+    else:
+        # For multiple-module use-case (or if output_file doesn't end with .py),
+        # assume output_file is really an output path for the parent dir
+        # (e.g. lib/python/pxr)
+        module_output_dir = os.path.join(output_file, moduleName)
+        module_output_file = os.path.join(module_output_dir, "__DOC.py")
+    output_files.append(module_output_file)
+assert len(output_files) == len(module_list)
+
+for module_output_file in output_files:
+    if os.path.isfile(module_output_file):
+        os.remove(module_output_file)
+
 #
 # If caller specified an additional path for python libs (for loading USD
 # modules, for example) add the path to sys.path
@@ -121,19 +147,10 @@
 # load provided python module(s) and find matching python
 # entities, and write matches to python docs output
 #
-packageName = GetArgValue(['--package', '-p'])
-modules = GetArgValue(['--module', '-m'])
-if not packageName:
-    Error("Required option --package not specified")
-if not modules:
-    Error("Required option --module not specified")
-
-moduleList = modules.split(",")
-for moduleName in moduleList:
+for moduleName, module_output_file in zip(module_list, output_files):
     # Loop through module list and create a Writer for each module to
     # load and generate the doc strings for the specific module
-    if not moduleName:
-        continue
+
     # Writer's constructor will verify provided package + module can be loaded
     writer = Writer(packageName, moduleName)
     Debug("Processing module %s" % moduleName)
@@ -146,13 +163,5 @@
         if use_cached_parsing:
             with open(pickle_path, "wb") as picklefile:
                 pickle.dump(docList, picklefile)
-    if len(moduleList) == 1 and output_file.endswith(".py"):
-        module_output_file = output_file
-    else:
-        # For multiple-module use-case (or if output_file doesn't end with .py),
-        # assume output_file is really an output path for the parent dir
-        # (e.g. lib/python/pxr)
-        module_output_dir = os.path.join(output_file, moduleName)
-        module_output_file = os.path.join(module_output_dir, "__DOC.py")
     writer.generate(module_output_file, docList)