Added a test to nail down the {token} substitution spec a tad. Added a docstring to describe the purpose of the _backport dir.

3 files changed, 12 insertions, 2 deletions

diff --git a/src/distutils2/_backport/__init__.py b/src/distutils2/_backport/__init__.py
index e69de29..c5227d3 100644
--- a/src/distutils2/_backport/__init__.py
+++ b/src/distutils2/_backport/__init__.py
@@ -0,0 +1,2 @@
+"""Things that will land in the Python 3.3 std lib but which we must drag along
+with us for now to support 2.x."""
diff --git a/src/distutils2/_backport/sysconfig.py b/src/distutils2/_backport/sysconfig.py
index f72ef5c..62ff8ca 100644
--- a/src/distutils2/_backport/sysconfig.py
+++ b/src/distutils2/_backport/sysconfig.py
@@ -75,7 +75,11 @@ if _PYTHON_BUILD:
 
 
 def _subst_vars(path, local_vars):
-    # simple curly-braces replacement
+    """In the string `path`, replace tokens like {some.thing} with the corresponding value from the map `local_vars`.
+    
+    If there is no corresponding value, leave the token unchanged.
+    
+    """
     def _replacer(matchobj):
         name = matchobj.group(1)
         if name in local_vars:
diff --git a/src/distutils2/_backport/tests/test_sysconfig.py b/src/distutils2/_backport/tests/test_sysconfig.py
index 5bc98cf..294ed5c 100644
--- a/src/distutils2/_backport/tests/test_sysconfig.py
+++ b/src/distutils2/_backport/tests/test_sysconfig.py
@@ -17,7 +17,7 @@ import distutils2._backport.sysconfig
 from distutils2._backport.sysconfig import (get_paths, get_platform,
                         get_config_vars, _expand_globals,
                        get_path, get_path_names,
-                       _get_default_scheme, _expand_vars,
+                       _get_default_scheme, _subst_vars, _expand_vars,
                        get_scheme_names, _CONFIG_FILE)
 
 class TestSysConfig(unittest2.TestCase):
@@ -87,6 +87,10 @@ class TestSysConfig(unittest2.TestCase):
         elif os.path.isdir(path):
             shutil.rmtree(path)
 
+    def test_var_expansion_pattern(self):
+        """Assert that the {curly brace token} expansion pattern counts the second { as part of the substitution key in expressions like {{something}."""
+        self.failUnlessEqual(_subst_vars('thing{{stuffvar}', {'{stuffvar': 'stuff'}), 'thingstuff')
+
     def test_get_paths(self):
         scheme = get_paths()
         default_scheme = _get_default_scheme()