catch error if networkx is not installed

network_extensions/igraphx/__init__.py

@@ -16,7 +16,10 @@ import uuid
 from itertools import product
 from collections import defaultdict, OrderedDict
 import numpy as np
-import networkx
+try:
+    import networkx
+except:
+    logging.warning("Cannot import networkx, functions using this library will not work!")
 from tqdm import tqdm
 import pylab