Index: build/type.py
===================================================================
--- build/type.py	(revision 75519)
+++ build/type.py	(working copy)
@@ -81,7 +81,7 @@
     __types [type] = entry
     
     if base_type:
-        __types [base_type]['derived'].append (type)
+        __types.setdefault(base_type, {}).setdefault('derived', []).append(type)
 
     if len (suffixes) > 0:
         # Generated targets of 'type' will use the first of 'suffixes'
Index: build_system.py
===================================================================
--- build_system.py	(revision 75519)
+++ build_system.py	(working copy)
@@ -524,7 +524,7 @@
         print "warning: For more configuration options, please consult"
         print "warning: http://boost.org/boost-build2/doc/html/bbv2/advanced/configuration.html"
 
-        toolset.using(dt, dtv)
+        using(dt, dtv)
 
     # Parse command line for targets and properties. Note that this requires
     # that all project files already be loaded.
Index: tools/common.py
===================================================================
--- tools/common.py	(revision 75519)
+++ tools/common.py	(working copy)
@@ -53,7 +53,7 @@
     if OS == "NT":
         # On Windows the case and capitalization of PATH is not always predictable, so
         # let's find out what variable name was really set.
-        for n in sys.environ:
+        for n in os.environ:
             if n.lower() == "path":
                 __executable_path_variable = n
                 break
@@ -99,7 +99,7 @@
     def __init__(self):
         self.used_ = set()
         self.all_ = set()
-        self.params = {}
+        self.params_ = {}
 
     def register(self, id):
         """
@@ -113,7 +113,7 @@
             errors.error("common: the configuration '$(id)' is in use")
 
         if id not in self.all_:
-            self.all_ += [id]
+            self.all_.add(id)
 
             # Indicate that a new configuration has been added.
             return True
@@ -133,7 +133,7 @@
             errors.error("common: the configuration '$(id)' is not known")
 
         if id not in self.used_:
-            self.used_ += [id]
+            self.used_.add(id)
 
             # indicate that the configuration has been marked as 'used'
             return True
@@ -150,7 +150,7 @@
 
     def get(self, id, param):
         """ Returns the value of a configuration parameter. """
-        self.params_.getdefault(param, {}).getdefault(id, None)
+        self.params_.get(param, {}).get(id)
 
     def set (self, id, param, value):
         """ Sets the value of a configuration parameter. """