call BasicObjectPathComponent with two positional args

quote test cases object paths appropriately
quote object components when stringifying, if needed
import pattern classes using *
If there is no special class, instantiate the basic stix2 pattern class

stix2/STIXPatternVisitor.py

@@ -11,14 +11,8 @@ from stix2patterns.validator import STIXPatternErrorListener
 
 from antlr4 import CommonTokenStream, InputStream
 
-from .patterns import (
-    BasicObjectPathComponent, BinaryConstant, BooleanConstant, FloatConstant,
-    FollowedByObservationExpression, HexConstant, IntegerConstant,
-    IsSubsetComparisonExpression, IsSupersetComparisonExpression,
-    ListObjectPathComponent, RepeatQualifier, StartStopQualifier,
-    StringConstant, TimestampConstant, WithinQualifier,
-)
-
+# need to import all classes because we need to access them via globals()
+from .patterns import *
 
 def collapse_lists(lists):
     result = []
@@ -30,11 +24,7 @@ def collapse_lists(lists):
     return result
 
 
-def quote_if_needed(x):
-    if x.find("-") != -1:
-        return "'" + x + "'"
-    else:
-        return x
+
 
 # This class defines a complete generic visitor for a parse tree produced by STIXPatternParser.
 
@@ -54,12 +44,16 @@ class STIXPatternVisitorForSTIX2(STIXPatternVisitor):
         super(STIXPatternVisitor, self).__init__()
 
     def get_class(self, class_name):
-        return STIXPatternVisitorForSTIX2.classes[class_name]
+        if class_name in STIXPatternVisitorForSTIX2.classes:
+            return STIXPatternVisitorForSTIX2.classes[class_name]
+        else:
+            return None
 
     def instantiate(self, klass_name, *args):
+        klass_to_instantiate = None
         if self.module_suffix:
             klass_to_instantiate = self.get_class(klass_name + "For" + self.module_suffix)
-        else:
+        if not klass_to_instantiate:
             # use the classes in python_stix2
             klass_to_instantiate = globals()[klass_name]
         return klass_to_instantiate(*args)
@@ -214,11 +208,11 @@ class STIXPatternVisitorForSTIX2(STIXPatternVisitor):
         while i < len(flat_list):
             current = flat_list[i]
             if i == len(flat_list)-1:
-                property_path.append(quote_if_needed(current))
+                property_path.append(current)
                 break
             next = flat_list[i+1]
             if isinstance(next, TerminalNode):
-                property_path.append(ListObjectPathComponent(current.property_name, next.getText()))
+                property_path.append(self.instantiate("ListObjectPathComponent", current.property_name, next.getText()))
                 i += 2
             else:
                 property_path.append(current)
@@ -237,7 +231,7 @@ class STIXPatternVisitorForSTIX2(STIXPatternVisitor):
         # if step.endswith("_ref"):
         #     return stix2.ReferenceObjectPathComponent(step)
         # else:
-        return BasicObjectPathComponent(step)
+        return self.instantiate("BasicObjectPathComponent", step, False)
 
     # Visit a parse tree produced by STIXPatternParser#indexPathStep.
     def visitIndexPathStep(self, ctx):
@@ -255,7 +249,7 @@ class STIXPatternVisitorForSTIX2(STIXPatternVisitor):
             # special case for hashes
             return children[1].value
         else:
-            return BasicObjectPathComponent(children[1].getText(), is_key=True)
+            return self.instantiate("BasicObjectPathComponent", children[1].getText(), True)
 
     # Visit a parse tree produced by STIXPatternParser#setLiteral.
     def visitSetLiteral(self, ctx):

stix2/patterns.py

@@ -13,6 +13,14 @@ def escape_quotes_and_backslashes(s):
     return s.replace(u'\\', u'\\\\').replace(u"'", u"\\'")
 
 
+def quote_if_needed(x):
+    if isinstance(x, str):
+        if x.find("-") != -1:
+            if not x.startswith("'"):
+                return "'" + x + "'"
+    return x
+
+
 class _Constant(object):
     pass
 
@@ -229,7 +237,10 @@ class _ObjectPathComponent(object):
             parse1 = component_name.split("[")
             return ListObjectPathComponent(parse1[0], parse1[1][:-1])
         else:
-            return BasicObjectPathComponent(component_name)
+            return BasicObjectPathComponent(component_name, False)
+
+    def __str__(self):
+        return quote_if_needed(self.property_name)
 
 
 class BasicObjectPathComponent(_ObjectPathComponent):
@@ -243,14 +254,11 @@ class BasicObjectPathComponent(_ObjectPathComponent):
         property_name (str): object property name
         is_key (bool): is dictionary key, default: False
     """
-    def __init__(self, property_name, is_key=False):
+    def __init__(self, property_name, is_key):
         self.property_name = property_name
         # TODO: set is_key to True if this component is a dictionary key
         # self.is_key = is_key
 
-    def __str__(self):
-        return self.property_name
-
 
 class ListObjectPathComponent(_ObjectPathComponent):
     """List object path component (for an observation or expression)
@@ -264,7 +272,7 @@ class ListObjectPathComponent(_ObjectPathComponent):
         self.index = index
 
     def __str__(self):
-        return "%s[%s]" % (self.property_name, self.index)
+        return "%s[%s]" % (quote_if_needed(self.property_name), self.index)
 
 
 class ReferenceObjectPathComponent(_ObjectPathComponent):
@@ -276,9 +284,6 @@ class ReferenceObjectPathComponent(_ObjectPathComponent):
     def __init__(self, reference_property_name):
         self.property_name = reference_property_name
 
-    def __str__(self):
-        return self.property_name
-
 
 class ObjectPath(object):
     """Pattern operand object (property) path
@@ -296,7 +301,7 @@ class ObjectPath(object):
         ]
 
     def __str__(self):
-        return "%s:%s" % (self.object_type_name, ".".join(["%s" % x for x in self.property_path]))
+        return "%s:%s" % (self.object_type_name, ".".join(["%s" % quote_if_needed(x) for x in self.property_path]))
 
     def merge(self, other):
         """Extend the object property with that of the supplied object property path"""

stix2/test/test_pattern_expressions.py

@@ -34,7 +34,7 @@ def test_boolean_expression_with_parentheses():
             "email-message",
             [
                 stix2.ReferenceObjectPathComponent("from_ref"),
-                stix2.BasicObjectPathComponent("value"),
+                stix2.BasicObjectPathComponent("value", False),
             ],
         ),
         stix2.StringConstant(".+\\@example\\.com$"),
@@ -159,18 +159,18 @@ def test_artifact_payload():
 
 
 def test_greater_than_python_constant():
-    exp1 = stix2.GreaterThanComparisonExpression("file:extensions.windows-pebinary-ext.sections[*].entropy", 7.0)
+    exp1 = stix2.GreaterThanComparisonExpression("file:extensions.'windows-pebinary-ext'.sections[*].entropy", 7.0)
     exp = stix2.ObservationExpression(exp1)
-    assert str(exp) == "[file:extensions.windows-pebinary-ext.sections[*].entropy > 7.0]"
+    assert str(exp) == "[file:extensions.'windows-pebinary-ext'.sections[*].entropy > 7.0]"
 
 
 def test_greater_than():
     exp1 = stix2.GreaterThanComparisonExpression(
-        "file:extensions.windows-pebinary-ext.sections[*].entropy",
+        "file:extensions.'windows-pebinary-ext'.sections[*].entropy",
         stix2.FloatConstant(7.0),
     )
     exp = stix2.ObservationExpression(exp1)
-    assert str(exp) == "[file:extensions.windows-pebinary-ext.sections[*].entropy > 7.0]"
+    assert str(exp) == "[file:extensions.'windows-pebinary-ext'.sections[*].entropy > 7.0]"
 
 
 def test_less_than():