bindings: (fixes #796) Gracefully exit when bindings are unavailable

examples/wireless/mixed-wired-wireless.py

@@ -51,7 +51,14 @@
 #           +----------------+                       +----------------+
 #
 
-from ns import ns
+try:
+    from ns import ns
+except ModuleNotFoundError:
+    raise SystemExit(
+        "Error: ns3 Python module not found;"
+        " Python bindings may not be enabled"
+        " or your PYTHONPATH might not be properly configured"
+    )
 
 # #
 # #  This function will be used below as a trace sink

examples/wireless/wifi-ap.py

@@ -22,7 +22,14 @@
 
 import sys
 
-from ns import ns
+try:
+    from ns import ns
+except ModuleNotFoundError:
+    raise SystemExit(
+        "Error: ns3 Python module not found;"
+        " Python bindings may not be enabled"
+        " or your PYTHONPATH might not be properly configured"
+    )
 
 # void
 # DevTxTrace (std::string context, Ptr<const Packet> p, Mac48Address address)