Continue to allow %s in settings valuesbaserock/sam/python3

We need to use the special 'LegacyInterpolation' class with Python 3's
'configparser' module, otherwise %-formats in config values get parsed
and can trigger a ValueError, which doesn't happen with Python 2.

1 files changed, 16 insertions, 3 deletions

diff --git a/cliapp/settings.py b/cliapp/settings.py
index de058c9..298cd6a 100644
--- a/cliapp/settings.py
+++ b/cliapp/settings.py
@@ -301,7 +301,20 @@ class Settings(object):
         self._add_default_settings()
 
         self._config_files = None
-        self._cp = configparser.ConfigParser()
+
+        self._cp = self._create_configparser()
+
+    def _create_configparser(self):
+        if sys.version_info[0] == 2:
+            cp = configparser.ConfigParser()
+        else:
+            # The default interpolation in Python 3 is
+            # configparser.BasicInterpolation. This class parses % symbols in
+            # the strings, which can break existing cliapp.settings users. The
+            # LegacyInterpolation class preserves the Python 2 behaviour.
+            cp = configparser.RawConfigParser(
+                interpolation=configparser.LegacyInterpolation())
+        return cp
 
     def _add_default_settings(self):
         self.string(['output'],
@@ -751,7 +764,7 @@ class Settings(object):
 
         '''
 
-        cp = configparser.ConfigParser()
+        cp = self._create_configparser()
         cp.add_section('config')
 
         for pathname in self.config_files:
@@ -787,7 +800,7 @@ class Settings(object):
         meanings it desires to the section names.
 
         '''
-        cp = configparser.ConfigParser()
+        cp = self._create_configparser()
         cp.add_section('config')
         for name in self._canonical_names:
             cp.set('config', name, self._settingses[name].format())