defining fuse_python_api made mandatory

Author: dzsekijo

example/hello.py

@@ -20,8 +20,6 @@
     raise RuntimeError, \
         "your fuse-py doesn't know of fuse.__version__, probably it's too old."
 
-# This setting is optional, but it ensures that this class will keep
-# working after a future API revision
 fuse.fuse_python_api = (0, 2)
 
 hello_path = '/hello'

example/xmp.py

@@ -24,8 +24,6 @@
     raise RuntimeError, \
         "your fuse-py doesn't know of fuse.__version__, probably it's too old."
 
-# This setting is optional, but it ensures that this class will keep
-# working after a future API revision
 fuse.fuse_python_api = (0, 2)
 
 fuse.feature_assert('stateful_files', 'has_init')

fuse.py

@@ -633,6 +633,24 @@ def __init__(self, *args, **kw):
         available options.)
         """
 
+        if not fuse_python_api and not compat_0_1:
+            raise RuntimeError, __name__ + """.fuse_python_api not defined.
+
+! Please define """ + __name__ + """.fuse_python_api internally (eg.
+! 
+! (1)  """ + __name__ + """.fuse_python_api = """ + `FUSE_PYTHON_API_VERSION` + """
+! 
+! ) or in the enviroment (eg. 
+! 
+! (2)  FUSE_PYTHON_API=0.1
+! 
+! ).
+!
+! If you are actually developing a filesystem, probably (1) is the way to go.
+! If you are using a filesystem written before 2007 Q2, probably (2) is what
+! you want."
+"""
+
         self.fuse_args = \
             'fuse_args' in kw and kw.pop('fuse_args') or FuseArgs()