From 4229c380a2be444cf617317608007b0cae44a603 Mon Sep 17 00:00:00 2001
From: Chris Lenk <clenk@mitre.org>
Date: Thu, 26 Apr 2018 10:20:46 -0400
Subject: [PATCH] Fix make_constant when value is already a constant

Fixes #171.
---
 stix2/patterns.py                      | 3 +++
 stix2/test/test_pattern_expressions.py | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/stix2/patterns.py b/stix2/patterns.py
index 23ce71b..3f9cbd9 100644
--- a/stix2/patterns.py
+++ b/stix2/patterns.py
@@ -147,6 +147,9 @@ class ListConstant(_Constant):
 
 
 def make_constant(value):
+    if isinstance(value, _Constant):
+        return value
+
     try:
         return parse_into_datetime(value)
     except ValueError:
diff --git a/stix2/test/test_pattern_expressions.py b/stix2/test/test_pattern_expressions.py
index 74a7d0f..14e3774 100644
--- a/stix2/test/test_pattern_expressions.py
+++ b/stix2/test/test_pattern_expressions.py
@@ -372,3 +372,9 @@ def test_invalid_startstop_qualifier():
         stix2.StartStopQualifier(datetime.date(2016, 6, 1),
                                  'foo')
     assert 'is not a valid argument for a Start/Stop Qualifier' in str(excinfo)
+
+
+def test_make_constant_already_a_constant():
+    str_const = stix2.StringConstant('Foo')
+    result = stix2.patterns.make_constant(str_const)
+    assert result is str_const