python-control
diff --git a/‎control/namedio.py‎
Lines changed: 12 additions & 3 deletions b/‎control/namedio.py‎
Lines changed: 12 additions & 3 deletions
diff --git a/‎control/tests/namedio_test.py‎
Lines changed: 9 additions & 0 deletions b/‎control/tests/namedio_test.py‎
Lines changed: 9 additions & 0 deletions
@@ -13,6 +13,7 @@
 
 __all__ = ['issiso', 'timebase', 'common_timebase', 'timebaseEqual',
            'isdtime', 'isctime']
+
 # Define module default parameter values
 _namedio_defaults = {
     'namedio.state_name_delim': '_',
@@ -57,6 +58,8 @@ def _name_or_default(self, name=None):
         if name is None:
             name = "sys[{}]".format(NamedIOSystem._idCounter)
             NamedIOSystem._idCounter += 1
+        elif re.match(r".*\..*", name):
+            raise ValueError(f"invalid system name '{name}' ('.' not allowed)")
         return name
 
     # Check if system name is generic
@@ -174,7 +177,6 @@ def copy(self, name=None, use_prefix_suffix=True):
         return newsys
 
     def set_inputs(self, inputs, prefix='u'):
-
         """Set the number/names of the system inputs.
 
         Parameters
@@ -258,7 +260,7 @@ def set_states(self, states, prefix='x'):
 
         """
         self.nstates, self.state_index = \
-            _process_signal_list(states, prefix=prefix)
+            _process_signal_list(states, prefix=prefix, allow_dot=True)
 
     def find_state(self, name):
         """Find the index for a state given its name (`None` if not found)"""
@@ -613,7 +615,7 @@ def _process_dt_keyword(keywords, defaults={}, static=False):
 
 
 # Utility function to parse a list of signals
-def _process_signal_list(signals, prefix='s'):
+def _process_signal_list(signals, prefix='s', allow_dot=False):
     if signals is None:
         # No information provided; try and make it up later
         return None, {}
@@ -624,10 +626,17 @@ def _process_signal_list(signals, prefix='s'):
 
     elif isinstance(signals, str):
         # Single string given => single signal with given name
+        if not allow_dot and re.match(r".*\..*", signals):
+            raise ValueError(
+                f"invalid signal name '{signals}' ('.' not allowed)")
         return 1, {signals: 0}
 
     elif all(isinstance(s, str) for s in signals):
         # Use the list of strings as the signal names
+        for signal in signals:
+            if not allow_dot and re.match(r".*\..*", signal):
+                raise ValueError(
+                    f"invalid signal name '{signal}' ('.' not allowed)")
         return len(signals), {signals[i]: i for i in range(len(signals))}
 
     else:
 
@@ -323,3 +323,12 @@ def test_find_signals():
     assert sys.find_outputs(['y', 'z']) == [0, 1, 2, 3]
     assert sys.find_outputs(['y[1:]', 'z']) == [1, 2, 3]
     assert sys.find_outputs(['y', 'z[:1]']) == [0, 1, 2, 3]
+
+
+# Invalid signal names
+def test_invalid_signal_names():
+    with pytest.raises(ValueError, match="invalid signal name"):
+        sys = ct.rss(4, inputs="input.signal", outputs=1)
+
+    with pytest.raises(ValueError, match="invalid system name"):
+        sys = ct.rss(4, inputs=1, outputs=1, name="system.subsys")