将参数传递给 SimpleHTTPRequestHandler

Question

I have to pass a parameter to SimpleHTTPRequestHandler class, so I used class factory to create a custom handler as below.

def RequestHandlerClass(application_path):    

  class CustomHandler(SimpleHTTPRequestHandler):

    def __init__(self, request, client_address, server):

        SimpleHTTPRequestHandler.__init__(self, request, client_address, server)
        self._file_1_done = False 
        self._file_2_done = False 
        self._application_path = application_path

    def _reset_flags(self):

        self._file_1_done = False 
        self._file_2_done = False 

    def do_GET(self):

        if (self.path == '/file1.qml'):
            self._file_1_done = True  

        if (self.path == '/file2.qml'):
            self._file_2_done = True 

        filepath = self._application_path + '/' + self.path  # Error here

        try:
            f = open(filepath) 
            self.send_response(200)
            self.end_headers()
            self.wfile.write(f.read())
            f.close()
        except IOError as e :
            self.send_error(404,'File Not Found: %s' % self.path)    


        if (self._file_1_done and self._file_2_done):
            self._reset_flags()  
            self.server.app_download_complete_event.set()
  return CustomHandler 

This is my httpserver using the custom handler

class PythonHtpServer(BaseHTTPServer.HTTPServer, threading.Thread):

  def __init__(self, port, serve_path):
    custom_request_handler_class = RequestHandlerClass(serve_path)
    BaseHTTPServer.HTTPServer.__init__(self, ('0.0.0.0', port), custom_request_handler_class)
    threading.Thread.__init__(self)
    self.app_download_complete_event = threading.Event()

  def run(self):
    self.serve_forever()

  def stop(self):
    self.shutdown()    

and I start the server with

http_server = PythonHtpServer(port = 8123, serve_path = '/application/main.qml')

The server starts, but I get this error

AttributeError: CustomHandler instance has no attribute '_application_path'

Basically, from the error, the server did start but I don't know why it is not creating the attributes ( or the init is not called ). Please tell me where I am going wrong. Any help would be welcome.

Answer 1

IMHO the simplest way is to make _application_path a static attribute of the class. It is declared only at class declaration time, and can be used transparently by instances of the class:

def RequestHandlerClass(application_path):    

  class CustomHandler(SimpleHTTPRequestHandler):

    _application_path = application_path   # static attribute

    def __init__(self, request, client_address, server):

        SimpleHTTPRequestHandler.__init__(self, request, client_address, server)
        self._file_1_done = False 
        self._file_2_done = False 

    def _reset_flags(self):
        ...

That way every new instance of the custom handler class will have access to the application path as self._application_path .

Answer 2

Conceptually, you've written something like this (in this eg, application_path ~= var ):

def createClass(var):
    class MyClass:
        def __init__(self):
            self.var = var
        def func(self):
            # use var in some way
            print (self.var)
    # Return class definition
    return MyClass

So the class is written to save the variable var when an instance of MyClass is created . However, by the time the function finishes, the variable is destroyed , and since the class only returns a class definition and not a class instance , an instance of MyClass does not get created by the time the original variable var is destroyed, and thus the variable var never actually gets saved by MyClass .

INSTEAD, you can add var as an argument to the MyClass.__init__ function, and create a generator class to handle creation of MyClass instances, like so:

class MyClass:
    def __init__(self, arg1, arg2, var):
        (self.arg1, self.arg2, self.var) = (arg1, arg2, var)
    # Insert other methods as usual

class MyClassGenerator:
    def __init__(self, var):
        self.var = var
    def make(self, arg1, arg2):
        return MyClass(arg1, arg2, var)

Answer 3

The issue here that BaseHttpRequestHandler (and thus its subclass, SimpleHttpRequestHandler) never makes it out of its __init__ method:

• HttpServer calls the SimpleHttpRequestHandler's constructor, which percolates up to the parent class' BaseHttpHandler__init__ ...
• BaseHttpHandler.__init__ calls handle , which is overridden in...
• BaseHttpRequestHandler.handle , which loops forever (given default options).

Thus, if you want to pass info along to your handler, you have to do it before calling the super's __init__ . I'm probably several years too late to help you, but for future readers, you can just switch the order of your __init__ :

class CustomHandler(http.server.SimpleHTTPRequestHandler):

  def __init__(self, *args, **kwargs):
    self._file_1_done = False 
    self._file_2_done = False
    self._application_path = application_path
    super().__init__(*args, **kwargs)

I'd probably also use functools.partial instead of wrapping the whole thing in a function:

class CustomHandler(http.server.SimpleHTTPRequestHandler):

  def __init__(self, application_path, *args, **kwargs):
    self._file_1_done = False 
    self._file_2_done = False
    self._application_path = application_path
    super().__init__(*args, **kwargs)

...

custom_request_handler_class = functools.partial(CustomHandler, serve_path)
BaseHTTPServer.HTTPServer(('0.0.0.0', port), custom_request_handler_class)

It's probably not a great idea to call super().__init__ at the end of your init in general (since it might mess up initialization), but here it seems like Python is kind of forcing your hand.