diff --git a/generator.py b/generator.py
index 7727679..dba12fd 100755
--- a/generator.py
+++ b/generator.py
@@ -31,6 +31,8 @@ quiet = True
 #######################################################################
 debug = 0
 onlyOverrides = False
+sourceDir = "."
+buildDir = "build"
 
 libvirt_headers = [
     "libvirt",
@@ -49,6 +51,11 @@ libvirt_headers = [
     "libvirt-stream",
 ]
 
+def openSourceFile(file: str, mode: str = "r", optional: bool = False):
+    path = os.path.join(sourceDir, file)
+    if optional and not os.path.exists(path):
+        return None
+    return open(path, mode)
 
 def parse(data: IO[str]) -> None:
     target = docParser()
@@ -853,7 +860,7 @@ def load_apis(module: str, api_xml: str):
 
     try:
         onlyOverrides = True
-        with open(override_api_xml) as stream:
+        with openSourceFile(override_api_xml) as stream:
             parse(stream)
     except IOError as msg:
         print(override_api_xml, ":", msg)
@@ -869,9 +876,9 @@ def emit_c_code(module: str) -> None:
 
     nb_wrap = 0
 
-    header_file = "build/%s.h" % module
-    export_file = "build/%s-export.c" % module
-    wrapper_file = "build/%s.c" % module
+    header_file = "%s/%s.h" % (buildDir, module)
+    export_file = "%s/%s-export.c" % (buildDir, module)
+    wrapper_file = "%s/%s.c" % (buildDir, module)
 
     include = open(header_file, "w")
     include.write("/* Generated by generator.py */\n\n")
@@ -885,7 +892,7 @@ def emit_c_code(module: str) -> None:
     wrapper.write("#include <Python.h>\n")
     wrapper.write("#include <libvirt/%s.h>\n" % (module,))
     wrapper.write("#include \"typewrappers.h\"\n")
-    wrapper.write("#include \"build/%s.h\"\n\n" % (module,))
+    wrapper.write("#include \"%s/%s.h\"\n\n" % (buildDir, module))
 
     for function in sorted(functions):
         if print_function_wrapper(package, function, wrapper, export, include):
@@ -1313,14 +1320,12 @@ def emit_py_code(module: str) -> None:
             info = (0, func, name, ret, args, file, mod)
             function_classes['None'].append(info)
 
-    classes_file = "build/%s.py" % package
+    classes_file = "%s/%s.py" % (buildDir, package)
     extra_file = "%s-override.py" % module
-    extra = None
+    extra = openSourceFile(extra_file, "r", True)
 
     classes = open(classes_file, "w")
 
-    if os.path.exists(extra_file):
-        extra = open(extra_file, "r")
     classes.write("#\n")
     classes.write("# WARNING WARNING WARNING WARNING\n")
     classes.write("#\n")
@@ -1629,8 +1634,8 @@ def emit_py_code(module: str) -> None:
                 classes.write("\n")
             # Append "<classname>.py" to class def, iff it exists
             class_override = "%s-override-%s.py" % (module, classname)
-            if os.path.exists(class_override):
-                extra = open(class_override, "r")
+            extra = openSourceFile(class_override, "r", True)
+            if extra:
                 classes.write("    #\n")
                 classes.write("    # %s methods from %s.py (hand coded)\n" % (classname, classname))
                 classes.write("    #\n")
@@ -1776,6 +1781,11 @@ if sys.argv[1] not in ["libvirt", "libvirt-lxc", "libvirt-qemu"]:
     print("ERROR: unknown module %s" % sys.argv[1])
     sys.exit(1)
 
+if len(sys.argv) == 6:
+    buildDir = sys.argv[5]
+if len(sys.argv) >= 5:
+    sourceDir = sys.argv[4]
+
 load_apis(sys.argv[1], sys.argv[2])
 
 if validate_functions() < 0:
@@ -1786,12 +1796,12 @@ if not os.path.exists("build"):
     os.mkdir("build")
 
 output = None
-if len(sys.argv) == 4:
+if len(sys.argv) >= 4:
     output = sys.argv[3]
-if output == "c" or output is None:
+if output == "c" or output == "c+py" or output is None:
     emit_c_code(sys.argv[1])
 
-if output == "py" or output is None:
+if output == "py" or output == "c+py" or output is None:
     emit_py_code(sys.argv[1])
 
 sys.exit(0)