GAE throwing error about commented out code.

The code is commented out in my source file. However, Google App Engine still complaints an error within the commented out code. What is happening?

Traceback (most recent call last): File "/base/alloc/tmpfs/dynamic_runtimes/python27/54c5883f70296ec8_unzipped/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1535, in call rv = self.handle_exception(request, response, e) File "/base/alloc/tmpfs/dynamic_runtimes/python27/54c5883f70296ec8_unzipped/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1529, in call rv = self.router.dispatch(request, response) File "/base/alloc/tmpfs/dynamic_runtimes/python27/54c5883f70296ec8_unzipped/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1278, in default_dispatcher return route.handler_adapter(request, response) File "/base/alloc/tmpfs/dynamic_runtimes/python27/54c5883f70296ec8_unzipped/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1102, in call return handler.dispatch() File "/base/alloc/tmpfs/dynamic_runtimes/python27/54c5883f70296ec8_unzipped/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 572, in dispatch return self.handle_exception(e, self.app.debug) File "/base/alloc/tmpfs/dynamic_runtimes/python27/54c5883f70296ec8_unzipped/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 570, in dispatch return method(*args, **kwargs) File "/base/data/home/apps/s~book-shelf453/20180111t113535.406864553480734286/app/account.py", line 159, in post ##labels_list = detect_labels(saved_photo['gs-path']) TypeError: can only join an iterable