Clean up sampler help

tupak/core/sampler.py

@@ -1909,7 +1909,11 @@ if utils.command_line_args.sampler_help:
         print('Help for sampler "{}":'.format(sampler))
         print(sampler_class.__doc__)
     else:
-        print('Requested sampler {} not implemented.')
+        if sampler == "None":
+            print('For help with a specific sampler, call sampler-help with '
+                  'the name of the sampler')
+        else:
+            print('Requested sampler {} not implemented'.format(sampler))
         print('Available samplers = {}'.format(implemented_samplers))
 
     sys.exit()

tupak/core/utils.py

@@ -435,7 +435,8 @@ def set_up_command_line_arguments():
                         help="Force clean data, never use cached data")
     parser.add_argument("-u", "--use-cached", action="store_true",
                         help="Force cached data and do not check its validity")
-    parser.add_argument("--sampler-help", help=("Print help for given sampler"))
+    parser.add_argument("--sampler-help", nargs='?', default=False,
+                        const='None', help="Print help for given sampler")
     parser.add_argument("-t", "--test", action="store_true",
                         help=("Used for testing only: don't run full PE, but"
                               " just check nothing breaks"))