When specifying locustfile fia url, output start of response text whe…

…n it wasnt valid python.

locust/argument_parser.py

@@ -162,13 +162,17 @@ def download_locustfile_from_url(url: str) -> str:
     """
     try:
         response = requests.get(url)
-        # Check if response is valid python code
-        ast.parse(response.text)
     except requests.exceptions.RequestException as e:
         sys.stderr.write(f"Failed to get locustfile from: {url}. Exception: {e}")
         sys.exit(1)
-    except SyntaxError:
-        sys.stderr.write(f"Failed to get locustfile from: {url}. Response is not valid python code.")
+    else:
+        try:
+            # Check if response is valid python code
+            ast.parse(response.text)
+        except SyntaxError:
+            sys.stderr.write(
+                f"Failed to get locustfile from: {url}. Response was not valid python code: '{response.text[:100]}'"
+            )
         sys.exit(1)
 
     with open(os.path.join(tempfile.gettempdir(), urlparse(url).path.split("/")[-1]), "w") as locustfile: