do not write variables beginning with '_'

Config.py

@@ -4,19 +4,20 @@ import os
 class Config:
     def __init__(self, filename):
         self.filename = filename
-        self.vars = {}
+        self.variables = {}
         if os.path.isfile(filename):
             f = open(filename, 'r')
-            exec(f.read(), self.vars)
+            exec(f.read(), self.variables)
 
     def write(self):
         f = open(self.filename, 'w')
-        for var in self.vars:
-            f.write("%s = %s\n" % (var, repr(self.vars[var])))
+        for var in self.variables:
+            if var[0] != '_':
+                f.write("%s = %s\n" % (var, repr(self.variables[var])))
         f.close()
 
     def get(self, var):
-        return self.vars[var] if var in self.vars else None
+        return self.variables[var] if var in self.variables else None
 
     def set(self, var, val):
-        self.vars[var] = val
+        self.variables[var] = val