bugfix: only load sample images when needed during model export

Summary:
this makes getting started with model export easier as downloading the appropriate coco annotations and images is not required.

Pull Request resolved: #4079

Reviewed By: itomatik

Differential Revision: D39821989

Pulled By: itomatik

fbshipit-source-id: d2a8869067c7e05d60997dc09a4bf8be6eb5b525

Author: supershabam

tools/deploy/export_model.py

@@ -214,15 +214,14 @@ def get_sample_inputs(args):
     DetectionCheckpointer(torch_model).resume_or_load(cfg.MODEL.WEIGHTS)
     torch_model.eval()
 
-    # get sample data
-    sample_inputs = get_sample_inputs(args)
-
     # convert and save model
     if args.export_method == "caffe2_tracing":
+        sample_inputs = get_sample_inputs(args)
         exported_model = export_caffe2_tracing(cfg, torch_model, sample_inputs)
     elif args.export_method == "scripting":
         exported_model = export_scripting(torch_model)
     elif args.export_method == "tracing":
+        sample_inputs = get_sample_inputs(args)
         exported_model = export_tracing(torch_model, sample_inputs)
 
     # run evaluation with the converted model