tornado.web — RequestHandler and Application classes · Tornado 4.3官方文档

### Navigation - [index](# "General Index") - [modules](# "Python Module Index") | - [next](# "tornado.template — Flexible output generation") | - [previous](# "Web framework") | - [Tornado 4.4.dev1 documentation](#) » - [Web framework](#) » # `tornado.web` — `RequestHandler` and `Application` classes `tornado.web` provides a simple web framework with asynchronousfeatures that allow it to scale to large numbers of open connections,making it ideal for [long polling](http://en.wikipedia.org/wiki/Push_technology#Long_polling) [http://en.wikipedia.org/wiki/Push_technology#Long_polling]. Here is a simple “Hello, world” example app: ~~~ import tornado.ioloop import tornado.web class MainHandler(tornado.web.RequestHandler): def get(self): self.write("Hello, world") if __name__ == "__main__": application = tornado.web.Application([ (r"/", MainHandler), ]) application.listen(8888) tornado.ioloop.IOLoop.current().start() ~~~ See the [*User's guide*](#) for additional information. ### Thread-safety notes In general, methods on [`RequestHandler`](# "tornado.web.RequestHandler") and elsewhere in Tornado arenot thread-safe. In particular, methods such as[`write()`](# "tornado.web.RequestHandler.write"), [`finish()`](# "tornado.web.RequestHandler.finish"), and[`flush()`](# "tornado.web.RequestHandler.flush") must only be called from the main thread. Ifyou use multiple threads it is important to use [`IOLoop.add_callback`](# "tornado.ioloop.IOLoop.add_callback")to transfer control back to the main thread before finishing therequest. ### Request handlers *class *`tornado.web.``RequestHandler`(*application*, *request*, ***kwargs*)[[source]](#) Base class for HTTP request handlers. Subclasses must define at least one of the methods defined in the“Entry points” section below. ### Entry points `RequestHandler.``initialize`()[[source]](#) Hook for subclass initialization. Called for each request. A dictionary passed as the third argument of a url spec will besupplied as keyword arguments to initialize(). Example: ~~~ class ProfileHandler(RequestHandler): def initialize(self, database): self.database = database def get(self, username): ... app = Application([ (r'/user/(.*)', ProfileHandler, dict(database=database)), ]) ~~~ `RequestHandler.``prepare`()[[source]](#) Called at the beginning of a request before [`get`](# "tornado.web.RequestHandler.get")/[`post`](# "tornado.web.RequestHandler.post")/etc. Override this method to perform common initialization regardlessof the request method. Asynchronous support: Decorate this method with [`gen.coroutine`](# "tornado.gen.coroutine")or [`return_future`](# "tornado.concurrent.return_future") to make it asynchronous (the[`asynchronous`](# "tornado.web.asynchronous") decorator cannot be used on [`prepare`](# "tornado.web.RequestHandler.prepare")).If this method returns a [`Future`](# "tornado.concurrent.Future") execution will not proceeduntil the [`Future`](# "tornado.concurrent.Future") is done. New in version 3.1: Asynchronous support. `RequestHandler.``on_finish`()[[source]](#) Called after the end of a request. Override this method to perform cleanup, logging, etc.This method is a counterpart to [`prepare`](# "tornado.web.RequestHandler.prepare"). `on_finish` maynot produce any output, as it is called after the responsehas been sent to the client. Implement any of the following methods (collectively known as theHTTP verb methods) to handle the corresponding HTTP method.These methods can be made asynchronous with one of the followingdecorators: [`gen.coroutine`](# "tornado.gen.coroutine"), [`return_future`](# "tornado.concurrent.return_future"), or [`asynchronous`](# "tornado.web.asynchronous"). The arguments to these methods come from the [`URLSpec`](# "tornado.web.URLSpec"): Anycapturing groups in the regular expression become arguments to theHTTP verb methods (keyword arguments if the group is named,positional arguments if its unnamed). To support a method not on this list, override the class variable`SUPPORTED_METHODS`: ~~~ class WebDAVHandler(RequestHandler): SUPPORTED_METHODS = RequestHandler.SUPPORTED_METHODS + ('PROPFIND',) def propfind(self): pass ~~~ `RequestHandler.``get`(**args*, ***kwargs*)[[source]](#)`RequestHandler.``head`(**args*, ***kwargs*)[[source]](#)`RequestHandler.``post`(**args*, ***kwargs*)[[source]](#)`RequestHandler.``delete`(**args*, ***kwargs*)[[source]](#)`RequestHandler.``patch`(**args*, ***kwargs*)[[source]](#)`RequestHandler.``put`(**args*, ***kwargs*)[[source]](#)`RequestHandler.``options`(**args*, ***kwargs*)[[source]](#) ### Input `RequestHandler.``get_argument`(*name*, *default=[]*, *strip=True*)[[source]](#) Returns the value of the argument with the given name. If default is not provided, the argument is considered to berequired, and we raise a [`MissingArgumentError`](# "tornado.web.MissingArgumentError") if it is missing. If the argument appears in the url more than once, we return thelast value. The returned value is always unicode. `RequestHandler.``get_arguments`(*name*, *strip=True*)[[source]](#) Returns a list of the arguments with the given name. If the argument is not present, returns an empty list. The returned values are always unicode. `RequestHandler.``get_query_argument`(*name*, *default=[]*, *strip=True*)[[source]](#) Returns the value of the argument with the given namefrom the request query string. If default is not provided, the argument is considered to berequired, and we raise a [`MissingArgumentError`](# "tornado.web.MissingArgumentError") if it is missing. If the argument appears in the url more than once, we return thelast value. The returned value is always unicode. New in version 3.2. `RequestHandler.``get_query_arguments`(*name*, *strip=True*)[[source]](#) Returns a list of the query arguments with the given name. If the argument is not present, returns an empty list. The returned values are always unicode. New in version 3.2. `RequestHandler.``get_body_argument`(*name*, *default=[]*, *strip=True*)[[source]](#) Returns the value of the argument with the given namefrom the request body. If default is not provided, the argument is considered to berequired, and we raise a [`MissingArgumentError`](# "tornado.web.MissingArgumentError") if it is missing. If the argument appears in the url more than once, we return thelast value. The returned value is always unicode. New in version 3.2. `RequestHandler.``get_body_arguments`(*name*, *strip=True*)[[source]](#) Returns a list of the body arguments with the given name. If the argument is not present, returns an empty list. The returned values are always unicode. New in version 3.2. `RequestHandler.``decode_argument`(*value*, *name=None*)[[source]](#) Decodes an argument from the request. The argument has been percent-decoded and is now a byte string.By default, this method decodes the argument as utf-8 and returnsa unicode string, but this may be overridden in subclasses. This method is used as a filter for both [`get_argument()`](# "tornado.web.RequestHandler.get_argument") and forvalues extracted from the url and passed to [`get()`](# "tornado.web.RequestHandler.get")/[`post()`](# "tornado.web.RequestHandler.post")/etc. The name of the argument is provided if known, but may be None(e.g. for unnamed groups in the url regex). `RequestHandler.``request` The [`tornado.httputil.HTTPServerRequest`](# "tornado.httputil.HTTPServerRequest") object containing additionalrequest parameters including e.g. headers and body data. `RequestHandler.``path_args``RequestHandler.``path_kwargs` The `path_args` and `path_kwargs` attributes contain thepositional and keyword arguments that are passed to the[HTTP verb methods](#). These attributes are setbefore those methods are called, so the values are availableduring [`prepare`](# "tornado.web.RequestHandler.prepare"). ### Output `RequestHandler.``set_status`(*status_code*, *reason=None*)[[source]](#) Sets the status code for our response. <table class="docutils field-list" frame="void" rules="none"><col class="field-name"/><col class="field-body"/><tbody valign="top"><tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple"><li>status_code (<a class="reference external" href="https://docs.python.org/3.4/library/functions.html#int" title="(in Python v3.4)">int</a> [https://docs.python.org/3.4/library/functions.html#int]) – Response status code. If <code class="docutils literal">reason</code> is <code class="docutils literal">None</code>,it must be present in <a class="reference external" href="https://docs.python.org/3.4/library/http.client.html#http.client.responses" title="(in Python v3.4)"><code class="xref py py-obj docutils literal">httplib.responses</code></a> [https://docs.python.org/3.4/library/http.client.html#http.client.responses].</li><li>reason (<a class="reference external" href="https://docs.python.org/3.4/library/string.html#module-string" title="(in Python v3.4)">string</a> [https://docs.python.org/3.4/library/string.html#module-string]) – Human-readable reason phrase describing the statuscode. If <code class="docutils literal">None</code>, it will be filled in from<a class="reference external" href="https://docs.python.org/3.4/library/http.client.html#http.client.responses" title="(in Python v3.4)"><code class="xref py py-obj docutils literal">httplib.responses</code></a> [https://docs.python.org/3.4/library/http.client.html#http.client.responses].</li></ul></td></tr></tbody></table> `RequestHandler.``set_header`(*name*, *value*)[[source]](#) Sets the given response header name and value. If a datetime is given, we automatically format it according to theHTTP specification. If the value is not a string, we convert it toa string. All header values are then encoded as UTF-8. `RequestHandler.``add_header`(*name*, *value*)[[source]](#) Adds the given response header and value. Unlike [`set_header`](# "tornado.web.RequestHandler.set_header"), [`add_header`](# "tornado.web.RequestHandler.add_header") may be called multiple timesto return multiple values for the same header. `RequestHandler.``clear_header`(*name*)[[source]](#) Clears an outgoing header, undoing a previous [`set_header`](# "tornado.web.RequestHandler.set_header") call. Note that this method does not apply to multi-valued headersset by [`add_header`](# "tornado.web.RequestHandler.add_header"). `RequestHandler.``set_default_headers`()[[source]](#) Override this to set HTTP headers at the beginning of the request. For example, this is the place to set a custom `Server` header.Note that setting such headers in the normal flow of requestprocessing may not do what you want, since headers may be resetduring error handling. `RequestHandler.``write`(*chunk*)[[source]](#) Writes the given chunk to the output buffer. To write the output to the network, use the flush() method below. If the given chunk is a dictionary, we write it as JSON and setthe Content-Type of the response to be `application/json`.(if you want to send JSON as a different `Content-Type`, callset_header *after* calling write()). Note that lists are not converted to JSON because of a potentialcross-site security vulnerability. All JSON output should bewrapped in a dictionary. More details at[http://haacked.com/archive/2009/06/25/json-hijacking.aspx/](http://haacked.com/archive/2009/06/25/json-hijacking.aspx/) and[https://github.com/facebook/tornado/issues/1009](https://github.com/facebook/tornado/issues/1009) `RequestHandler.``flush`(*include_footers=False*, *callback=None*)[[source]](#) Flushes the current output buffer to the network. The `callback` argument, if given, can be used for flow control:it will be run when all flushed data has been written to the socket.Note that only one flush callback can be outstanding at a time;if another flush occurs before the previous flush's callbackhas been run, the previous callback will be discarded. Changed in version 4.0: Now returns a [`Future`](# "tornado.concurrent.Future") if no callback is given. `RequestHandler.``finish`(*chunk=None*)[[source]](#) Finishes this response, ending the HTTP request. `RequestHandler.``render`(*template_name*, ***kwargs*)[[source]](#) Renders the template with the given arguments as the response. `RequestHandler.``render_string`(*template_name*, ***kwargs*)[[source]](#) Generate the given template with the given arguments. We return the generated byte string (in utf8). To generate andwrite a template as a response, use render() above. `RequestHandler.``get_template_namespace`()[[source]](#) Returns a dictionary to be used as the default template namespace. May be overridden by subclasses to add or modify values. The results of this method will be combined with additionaldefaults in the [`tornado.template`](# "tornado.template") module and keyword argumentsto [`render`](# "tornado.web.RequestHandler.render") or [`render_string`](# "tornado.web.RequestHandler.render_string"). `RequestHandler.``redirect`(*url*, *permanent=False*, *status=None*)[[source]](#) Sends a redirect to the given (optionally relative) URL. If the `status` argument is specified, that value is used as theHTTP status code; otherwise either 301 (permanent) or 302(temporary) is chosen based on the `permanent` argument.The default is 302 (temporary). `RequestHandler.``send_error`(*status_code=500*, ***kwargs*)[[source]](#) Sends the given HTTP error code to the browser. If [`flush()`](# "tornado.web.RequestHandler.flush") has already been called, it is not possible to sendan error, so this method will simply terminate the response.If output has been written but not yet flushed, it will be discardedand replaced with the error page. Override [`write_error()`](# "tornado.web.RequestHandler.write_error") to customize the error page that is returned.Additional keyword arguments are passed through to [`write_error`](# "tornado.web.RequestHandler.write_error"). `RequestHandler.``write_error`(*status_code*, ***kwargs*)[[source]](#) Override to implement custom error pages. `write_error` may call [`write`](# "tornado.web.RequestHandler.write"), [`render`](# "tornado.web.RequestHandler.render"), [`set_header`](# "tornado.web.RequestHandler.set_header"), etcto produce output as usual. If this error was caused by an uncaught exception (includingHTTPError), an `exc_info` triple will be available as`kwargs["exc_info"]`. Note that this exception may not bethe “current” exception for purposes of methods like`sys.exc_info()` or `traceback.format_exc`. `RequestHandler.``clear`()[[source]](#) Resets all headers and content for this response. `RequestHandler.``data_received`(*chunk*)[[source]](#) Implement this method to handle streamed request data. Requires the [`stream_request_body`](# "tornado.web.stream_request_body") decorator. ### Cookies `RequestHandler.``cookies` An alias for[`self.request.cookies`](# "tornado.httputil.HTTPServerRequest.cookies"). `RequestHandler.``get_cookie`(*name*, *default=None*)[[source]](#) Gets the value of the cookie with the given name, else default. `RequestHandler.``set_cookie`(*name*, *value*, *domain=None*, *expires=None*, *path='/'*, *expires_days=None*, ***kwargs*)[[source]](#) Sets the given cookie name/value with the given options. Additional keyword arguments are set on the Cookie.Morseldirectly.See [http://docs.python.org/library/cookie.html#morsel-objects](http://docs.python.org/library/cookie.html#morsel-objects)for available attributes. `RequestHandler.``clear_cookie`(*name*, *path='/'*, *domain=None*)[[source]](#) Deletes the cookie with the given name. Due to limitations of the cookie protocol, you must pass the samepath and domain to clear a cookie as were used when that cookiewas set (but there is no way to find out on the server sidewhich values were used for a given cookie). `RequestHandler.``clear_all_cookies`(*path='/'*, *domain=None*)[[source]](#) Deletes all the cookies the user sent with this request. See [`clear_cookie`](# "tornado.web.RequestHandler.clear_cookie") for more information on the path and domainparameters. Changed in version 3.2: Added the `path` and `domain` parameters. `RequestHandler.``get_secure_cookie`(*name*, *value=None*, *max_age_days=31*, *min_version=None*)[[source]](#) Returns the given signed cookie if it validates, or None. The decoded cookie value is returned as a byte string (unlike[`get_cookie`](# "tornado.web.RequestHandler.get_cookie")). Changed in version 3.2.1: Added the `min_version` argument. Introduced cookie version 2;both versions 1 and 2 are accepted by default. `RequestHandler.``get_secure_cookie_key_version`(*name*, *value=None*)[[source]](#) Returns the signing key version of the secure cookie. The version is returned as int. `RequestHandler.``set_secure_cookie`(*name*, *value*, *expires_days=30*, *version=None*, ***kwargs*)[[source]](#) Signs and timestamps a cookie so it cannot be forged. You must specify the `cookie_secret` setting in your Applicationto use this method. It should be a long, random sequence of bytesto be used as the HMAC secret for the signature. To read a cookie set with this method, use [`get_secure_cookie()`](# "tornado.web.RequestHandler.get_secure_cookie"). Note that the `expires_days` parameter sets the lifetime of thecookie in the browser, but is independent of the `max_age_days`parameter to [`get_secure_cookie`](# "tornado.web.RequestHandler.get_secure_cookie"). Secure cookies may contain arbitrary byte values, not just unicodestrings (unlike regular cookies) Changed in version 3.2.1: Added the `version` argument. Introduced cookie version 2and made it the default. `RequestHandler.``create_signed_value`(*name*, *value*, *version=None*)[[source]](#) Signs and timestamps a string so it cannot be forged. Normally used via set_secure_cookie, but provided as a separatemethod for non-cookie uses. To decode a value not storedas a cookie use the optional value argument to get_secure_cookie. Changed in version 3.2.1: Added the `version` argument. Introduced cookie version 2and made it the default. `tornado.web.``MIN_SUPPORTED_SIGNED_VALUE_VERSION`* = 1* The oldest signed value version supported by this version of Tornado. Signed values older than this version cannot be decoded. New in version 3.2.1. `tornado.web.``MAX_SUPPORTED_SIGNED_VALUE_VERSION`* = 2* The newest signed value version supported by this version of Tornado. Signed values newer than this version cannot be decoded. New in version 3.2.1. `tornado.web.``DEFAULT_SIGNED_VALUE_VERSION`* = 2* The signed value version produced by [`RequestHandler.create_signed_value`](# "tornado.web.RequestHandler.create_signed_value"). May be overridden by passing a `version` keyword argument. New in version 3.2.1. `tornado.web.``DEFAULT_SIGNED_VALUE_MIN_VERSION`* = 1* The oldest signed value accepted by [`RequestHandler.get_secure_cookie`](# "tornado.web.RequestHandler.get_secure_cookie"). May be overridden by passing a `min_version` keyword argument. New in version 3.2.1. ### Other `RequestHandler.``application` The [`Application`](# "tornado.web.Application") object serving this request `RequestHandler.``check_etag_header`()[[source]](#) Checks the `Etag` header against requests's `If-None-Match`. Returns `True` if the request's Etag matches and a 304 should bereturned. For example: ~~~ self.set_etag_header() if self.check_etag_header(): self.set_status(304) return ~~~ This method is called automatically when the request is finished,but may be called earlier for applications that override[`compute_etag`](# "tornado.web.RequestHandler.compute_etag") and want to do an early check for `If-None-Match`before completing the request. The `Etag` header should be set(perhaps with [`set_etag_header`](# "tornado.web.RequestHandler.set_etag_header")) before calling this method. `RequestHandler.``check_xsrf_cookie`()[[source]](#) Verifies that the `_xsrf` cookie matches the `_xsrf` argument. To prevent cross-site request forgery, we set an `_xsrf`cookie and include the same value as a non-cookiefield with all `POST` requests. If the two do not match, wereject the form submission as a potential forgery. The `_xsrf` value may be set as either a form field named `_xsrf`or in a custom HTTP header named `X-XSRFToken` or `X-CSRFToken`(the latter is accepted for compatibility with Django). See [http://en.wikipedia.org/wiki/Cross-site_request_forgery](http://en.wikipedia.org/wiki/Cross-site_request_forgery) Prior to release 1.1.1, this check was ignored if the HTTP header`X-Requested-With: XMLHTTPRequest` was present. This exceptionhas been shown to be insecure and has been removed. For moreinformation please see[http://www.djangoproject.com/weblog/2011/feb/08/security/](http://www.djangoproject.com/weblog/2011/feb/08/security/)[http://weblog.rubyonrails.org/2011/2/8/csrf-protection-bypass-in-ruby-on-rails](http://weblog.rubyonrails.org/2011/2/8/csrf-protection-bypass-in-ruby-on-rails) Changed in version 3.2.2: Added support for cookie version 2. Both versions 1 and 2 aresupported. `RequestHandler.``compute_etag`()[[source]](#) Computes the etag header to be used for this request. By default uses a hash of the content written so far. May be overridden to provide custom etag implementations,or may return None to disable tornado's default etag support. `RequestHandler.``create_template_loader`(*template_path*)[[source]](#) Returns a new template loader for the given path. May be overridden by subclasses. By default returns adirectory-based loader on the given path, using the`autoescape` and `template_whitespace` applicationsettings. If a `template_loader` application setting issupplied, uses that instead. `RequestHandler.``current_user` The authenticated user for this request. This is set in one of two ways: - A subclass may override [`get_current_user()`](# "tornado.web.RequestHandler.get_current_user"), which will be calledautomatically the first time `self.current_user` is accessed.[`get_current_user()`](# "tornado.web.RequestHandler.get_current_user") will only be called once per request,and is cached for future access: ~~~ def get_current_user(self): user_cookie = self.get_secure_cookie("user") if user_cookie: return json.loads(user_cookie) return None ~~~ - It may be set as a normal variable, typically from an overridden[`prepare()`](# "tornado.web.RequestHandler.prepare"): ~~~ @gen.coroutine def prepare(self): user_id_cookie = self.get_secure_cookie("user_id") if user_id_cookie: self.current_user = yield load_user(user_id_cookie) ~~~ Note that [`prepare()`](# "tornado.web.RequestHandler.prepare") may be a coroutine while [`get_current_user()`](# "tornado.web.RequestHandler.get_current_user")may not, so the latter form is necessary if loading the user requiresasynchronous operations. The user object may any type of the application's choosing. `RequestHandler.``get_browser_locale`(*default='en_US'*)[[source]](#) Determines the user's locale from `Accept-Language` header. See [http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4](http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4) `RequestHandler.``get_current_user`()[[source]](#) Override to determine the current user from, e.g., a cookie. This method may not be a coroutine. `RequestHandler.``get_login_url`()[[source]](#) Override to customize the login URL based on the request. By default, we use the `login_url` application setting. `RequestHandler.``get_status`()[[source]](#) Returns the status code for our response. `RequestHandler.``get_template_path`()[[source]](#) Override to customize template path for each handler. By default, we use the `template_path` application setting.Return None to load templates relative to the calling file. `RequestHandler.``get_user_locale`()[[source]](#) Override to determine the locale from the authenticated user. If None is returned, we fall back to [`get_browser_locale()`](# "tornado.web.RequestHandler.get_browser_locale"). This method should return a [`tornado.locale.Locale`](# "tornado.locale.Locale") object,most likely obtained via a call like `tornado.locale.get("en")` `RequestHandler.``locale` The locale for the current session. Determined by either [`get_user_locale`](# "tornado.web.RequestHandler.get_user_locale"), which you can override toset the locale based on, e.g., a user preference stored in adatabase, or [`get_browser_locale`](# "tornado.web.RequestHandler.get_browser_locale"), which uses the `Accept-Language`header. `RequestHandler.``log_exception`(*typ*, *value*, *tb*)[[source]](#) Override to customize logging of uncaught exceptions. By default logs instances of [`HTTPError`](# "tornado.web.HTTPError") as warnings withoutstack traces (on the `tornado.general` logger), and allother exceptions as errors with stack traces (on the`tornado.application` logger). New in version 3.1. `RequestHandler.``on_connection_close`()[[source]](#) Called in async handlers if the client closed the connection. Override this to clean up resources associated withlong-lived connections. Note that this method is called only ifthe connection was closed during asynchronous processing; if youneed to do cleanup after every request override [`on_finish`](# "tornado.web.RequestHandler.on_finish")instead. Proxies may keep a connection open for a time (perhapsindefinitely) after the client has gone away, so this methodmay not be called promptly after the end user closes theirconnection. `RequestHandler.``require_setting`(*name*, *feature='this feature'*)[[source]](#) Raises an exception if the given app setting is not defined. `RequestHandler.``reverse_url`(*name*, **args*)[[source]](#) Alias for [`Application.reverse_url`](# "tornado.web.Application.reverse_url"). `RequestHandler.``set_etag_header`()[[source]](#) Sets the response's Etag header using `self.compute_etag()`. Note: no header will be set if `compute_etag()` returns `None`. This method is called automatically when the request is finished. `RequestHandler.``settings` An alias for [`self.application.settings`](# "tornado.web.Application.settings"). `RequestHandler.``static_url`(*path*, *include_host=None*, ***kwargs*)[[source]](#) Returns a static URL for the given relative static file path. This method requires you set the `static_path` setting in yourapplication (which specifies the root directory of your staticfiles). This method returns a versioned url (by default appending`?v=<signature>`), which allows the static files to becached indefinitely. This can be disabled by passing`include_version=False` (in the default implementation;other static file implementations are not required to supportthis, but they may support other options). By default this method returns URLs relative to the currenthost, but if `include_host` is true the URL returned will beabsolute. If this handler has an `include_host` attribute,that value will be used as the default for all [`static_url`](# "tornado.web.RequestHandler.static_url")calls that do not pass `include_host` as a keyword argument. `RequestHandler.``xsrf_form_html`()[[source]](#) An HTML `<input/>` element to be included with all POST forms. It defines the `_xsrf` input value, which we check on all POSTrequests to prevent cross-site request forgery. If you have setthe `xsrf_cookies` application setting, you must include thisHTML within all of your HTML forms. In a template, this method should be called with `{% modulexsrf_form_html() %}` See [`check_xsrf_cookie()`](# "tornado.web.RequestHandler.check_xsrf_cookie") above for more information. `RequestHandler.``xsrf_token` The XSRF-prevention token for the current user/session. To prevent cross-site request forgery, we set an ‘_xsrf' cookieand include the same ‘_xsrf' value as an argument with all POSTrequests. If the two do not match, we reject the form submissionas a potential forgery. See [http://en.wikipedia.org/wiki/Cross-site_request_forgery](http://en.wikipedia.org/wiki/Cross-site_request_forgery) Changed in version 3.2.2: The xsrf token will now be have a random mask applied in everyrequest, which makes it safe to include the token in pagesthat are compressed. See [http://breachattack.com](http://breachattack.com) for moreinformation on the issue fixed by this change. Old (version 1)cookies will be converted to version 2 when this method is calledunless the `xsrf_cookie_version`[`Application`](# "tornado.web.Application") setting isset to 1. Changed in version 4.3: The `xsrf_cookie_kwargs`[`Application`](# "tornado.web.Application") setting may beused to supply additional cookie options (which will bepassed directly to [`set_cookie`](# "tornado.web.RequestHandler.set_cookie")). For example,`xsrf_cookie_kwargs=dict(httponly=True, secure=True)`will set the `secure` and `httponly` flags on the`_xsrf` cookie. ### Application configuration *class *`tornado.web.``Application`(*handlers=None*, *default_host=''*, *transforms=None*, ***settings*)[[source]](#) A collection of request handlers that make up a web application. Instances of this class are callable and can be passed directly toHTTPServer to serve the application: ~~~ application = web.Application([ (r"/", MainPageHandler), ]) http_server = httpserver.HTTPServer(application) http_server.listen(8080) ioloop.IOLoop.current().start() ~~~ The constructor for this class takes in a list of [`URLSpec`](# "tornado.web.URLSpec") objectsor (regexp, request_class) tuples. When we receive requests, weiterate over the list in order and instantiate an instance of thefirst request class whose regexp matches the request path.The request class can be specified as either a class object or a(fully-qualified) name. Each tuple can contain additional elements, which correspond to thearguments to the [`URLSpec`](# "tornado.web.URLSpec") constructor. (Prior to Tornado 3.2,only tuples of two or three elements were allowed). A dictionary may be passed as the third element of the tuple,which will be used as keyword arguments to the handler'sconstructor and [`initialize`](# "tornado.web.RequestHandler.initialize") method. This patternis used for the [`StaticFileHandler`](# "tornado.web.StaticFileHandler") in this example (note that a[`StaticFileHandler`](# "tornado.web.StaticFileHandler") can be installed automatically with thestatic_path setting described below): ~~~ application = web.Application([ (r"/static/(.*)", web.StaticFileHandler, {"path": "/var/www"}), ]) ~~~ We support virtual hosts with the [`add_handlers`](# "tornado.web.Application.add_handlers") method, which takes ina host regular expression as the first argument: ~~~ application.add_handlers(r"www\.myhost\.com", [ (r"/article/([0-9]+)", ArticleHandler), ]) ~~~ You can serve static files by sending the `static_path` settingas a keyword argument. We will serve those files from the`/static/` URI (this is configurable with the`static_url_prefix` setting), and we will serve `/favicon.ico`and `/robots.txt` from the same directory. A custom subclass of[`StaticFileHandler`](# "tornado.web.StaticFileHandler") can be specified with the`static_handler_class` setting. `settings` Additional keyword arguments passed to the constructor aresaved in the [`settings`](# "tornado.web.Application.settings") dictionary, and are often referred toin documentation as “application settings”. Settings areused to customize various aspects of Tornado (although insome cases richer customization is possible by overridingmethods in a subclass of [`RequestHandler`](# "tornado.web.RequestHandler")). Someapplications also like to use the [`settings`](# "tornado.web.Application.settings") dictionary as away to make application-specific settings available tohandlers without using global variables. Settings used inTornado are described below. General settings: - `autoreload`: If `True`, the server process will restartwhen any source files change, as described in [Debug mode and automatic reloading](#).This option is new in Tornado 3.2; previously this functionalitywas controlled by the `debug` setting. - `debug`: Shorthand for several debug mode settings,described in [Debug mode and automatic reloading](#). Setting `debug=True` isequivalent to `autoreload=True`, `compiled_template_cache=False`,`static_hash_cache=False`, `serve_traceback=True`. - `default_handler_class` and `default_handler_args`:This handler will be used if no other match is found;use this to implement custom 404 pages (new in Tornado 3.2). - `compress_response`: If `True`, responses in textual formatswill be compressed automatically. New in Tornado 4.0. - `gzip`: Deprecated alias for `compress_response` sinceTornado 4.0. - `log_function`: This function will be called at the endof every request to log the result (with one argument, the[`RequestHandler`](# "tornado.web.RequestHandler") object). The default implementationwrites to the [`logging`](https://docs.python.org/3.4/library/logging.html#module-logging "(in Python v3.4)") [https://docs.python.org/3.4/library/logging.html#module-logging] module's root logger. May also becustomized by overriding [`Application.log_request`](# "tornado.web.Application.log_request"). - `serve_traceback`: If true, the default error pagewill include the traceback of the error. This option is new inTornado 3.2; previously this functionality was controlled bythe `debug` setting. - `ui_modules` and `ui_methods`: May be set to a mappingof [`UIModule`](# "tornado.web.UIModule") or UI methods to be made available to templates.May be set to a module, dictionary, or a list of modulesand/or dicts. See [UI modules](#) for more details. Authentication and security settings: - `cookie_secret`: Used by [`RequestHandler.get_secure_cookie`](# "tornado.web.RequestHandler.get_secure_cookie")and [`set_secure_cookie`](# "tornado.web.RequestHandler.set_secure_cookie") to sign cookies. - `key_version`: Used by requestHandler [`set_secure_cookie`](# "tornado.web.RequestHandler.set_secure_cookie")to sign cookies with a specific key when `cookie_secret`is a key dictionary. - `login_url`: The [`authenticated`](# "tornado.web.authenticated") decorator will redirectto this url if the user is not logged in. Can be furthercustomized by overriding [`RequestHandler.get_login_url`](# "tornado.web.RequestHandler.get_login_url") - `xsrf_cookies`: If true, [Cross-site request forgery protection](#) will be enabled. - `xsrf_cookie_version`: Controls the version of new XSRFcookies produced by this server. Should generally be leftat the default (which will always be the highest supportedversion), but may be set to a lower value temporarilyduring version transitions. New in Tornado 3.2.2, whichintroduced XSRF cookie version 2. - `xsrf_cookie_kwargs`: May be set to a dictionary ofadditional arguments to be passed to [`RequestHandler.set_cookie`](# "tornado.web.RequestHandler.set_cookie")for the XSRF cookie. - `twitter_consumer_key`, `twitter_consumer_secret`,`friendfeed_consumer_key`, `friendfeed_consumer_secret`,`google_consumer_key`, `google_consumer_secret`,`facebook_api_key`, `facebook_secret`: Used in the[`tornado.auth`](# "tornado.auth") module to authenticate to various APIs. Template settings: - `autoescape`: Controls automatic escaping for templates.May be set to `None` to disable escaping, or to the *name*of a function that all output should be passed through.Defaults to `"xhtml_escape"`. Can be changed on a per-templatebasis with the `{% autoescape %}` directive. - `compiled_template_cache`: Default is `True`; if `False`templates will be recompiled on every request. This optionis new in Tornado 3.2; previously this functionality was controlledby the `debug` setting. - `template_path`: Directory containing template files. Can befurther customized by overriding [`RequestHandler.get_template_path`](# "tornado.web.RequestHandler.get_template_path") - `template_loader`: Assign to an instance of[`tornado.template.BaseLoader`](# "tornado.template.BaseLoader") to customize template loading.If this setting is used the `template_path` and `autoescape`settings are ignored. Can be further customized by overriding[`RequestHandler.create_template_loader`](# "tornado.web.RequestHandler.create_template_loader"). - `template_whitespace`: Controls handling of whitespace intemplates; see [`tornado.template.filter_whitespace`](# "tornado.template.filter_whitespace") for allowedvalues. New in Tornado 4.3. Static file settings: - `static_hash_cache`: Default is `True`; if `False`static urls will be recomputed on every request. This optionis new in Tornado 3.2; previously this functionality was controlledby the `debug` setting. - `static_path`: Directory from which static files will beserved. - `static_url_prefix`: Url prefix for static files,defaults to `"/static/"`. - `static_handler_class`, `static_handler_args`: May be set touse a different handler for static files instead of the default[`tornado.web.StaticFileHandler`](# "tornado.web.StaticFileHandler"). `static_handler_args`, if set,should be a dictionary of keyword arguments to be passed to thehandler's `initialize` method. `listen`(*port*, *address=''*, ***kwargs*)[[source]](#) Starts an HTTP server for this application on the given port. This is a convenience alias for creating an [`HTTPServer`](# "tornado.httpserver.HTTPServer")object and calling its listen method. Keyword arguments notsupported by [`HTTPServer.listen`](# "tornado.tcpserver.TCPServer.listen") are passed to the[`HTTPServer`](# "tornado.httpserver.HTTPServer") constructor. For advanced uses(e.g. multi-process mode), do not use this method; create an[`HTTPServer`](# "tornado.httpserver.HTTPServer") and call its[`TCPServer.bind`](# "tornado.tcpserver.TCPServer.bind")/[`TCPServer.start`](# "tornado.tcpserver.TCPServer.start") methods directly. Note that after calling this method you still need to call`IOLoop.current().start()` to start the server. Returns the [`HTTPServer`](# "tornado.httpserver.HTTPServer") object. Changed in version 4.3: Now returns the [`HTTPServer`](# "tornado.httpserver.HTTPServer") object. `add_handlers`(*host_pattern*, *host_handlers*)[[source]](#) Appends the given handlers to our handler list. Host patterns are processed sequentially in the order they wereadded. All matching patterns will be considered. `reverse_url`(*name*, **args*)[[source]](#) Returns a URL path for handler named `name` The handler must be added to the application as a named [`URLSpec`](# "tornado.web.URLSpec"). Args will be substituted for capturing groups in the [`URLSpec`](# "tornado.web.URLSpec") regex.They will be converted to strings if necessary, encoded as utf8,and url-escaped. `log_request`(*handler*)[[source]](#) Writes a completed HTTP request to the logs. By default writes to the python root logger. To changethis behavior either subclass Application and override this method,or pass a function in the application settings dictionary as`log_function`. *class *`tornado.web.``URLSpec`(*pattern*, *handler*, *kwargs=None*, *name=None*)[[source]](#) Specifies mappings between URLs and handlers. Parameters: - `pattern`: Regular expression to be matched. Any capturinggroups in the regex will be passed in to the handler'sget/post/etc methods as arguments (by keyword if named, byposition if unnamed. Named and unnamed capturing groups maymay not be mixed in the same rule). - `handler`: [`RequestHandler`](# "tornado.web.RequestHandler") subclass to be invoked. - `kwargs` (optional): A dictionary of additional argumentsto be passed to the handler's constructor. - `name` (optional): A name for this handler. Used by[`Application.reverse_url`](# "tornado.web.Application.reverse_url"). The `URLSpec` class is also available under the name `tornado.web.url`. ### Decorators `tornado.web.``asynchronous`(*method*)[[source]](#) Wrap request handler methods with this if they are asynchronous. This decorator is for callback-style asynchronous methods; forcoroutines, use the `@gen.coroutine` decorator without`@asynchronous`. (It is legal for legacy reasons to use the twodecorators together provided `@asynchronous` is first, but`@asynchronous` will be ignored in this case) This decorator should only be applied to the [HTTP verbmethods](#); its behavior is undefined for any other method.This decorator does not *make* a method asynchronous; it tellsthe framework that the method *is* asynchronous. For this decoratorto be useful the method must (at least sometimes) do somethingasynchronous. If this decorator is given, the response is not finished when themethod returns. It is up to the request handler to call[`self.finish()`](# "tornado.web.RequestHandler.finish") to finish the HTTPrequest. Without this decorator, the request is automaticallyfinished when the `get()` or `post()` method returns. Example: ~~~ class MyRequestHandler(RequestHandler): @asynchronous def get(self): http = httpclient.AsyncHTTPClient() http.fetch("http://friendfeed.com/", self._on_download) def _on_download(self, response): self.write("Downloaded!") self.finish() ~~~ Changed in version 3.1: The ability to use `@gen.coroutine` without `@asynchronous`. Changed in version 4.3: Returning anything but `None` or ayieldable object from a method decorated with `@asynchronous`is an error. Such return values were previously ignored silently. `tornado.web.``authenticated`(*method*)[[source]](#) Decorate methods with this to require that the user be logged in. If the user is not logged in, they will be redirected to the configured[`login url`](# "tornado.web.RequestHandler.get_login_url"). If you configure a login url with a query parameter, Tornado willassume you know what you're doing and use it as-is. If not, itwill add a [`next`](https://docs.python.org/3.4/library/functions.html#next "(in Python v3.4)") [https://docs.python.org/3.4/library/functions.html#next] parameter so the login page knows where to sendyou once you're logged in. `tornado.web.``addslash`(*method*)[[source]](#) Use this decorator to add a missing trailing slash to the request path. For example, a request to `/foo` would redirect to `/foo/` with thisdecorator. Your request handler mapping should use a regular expressionlike `r'/foo/?'` in conjunction with using the decorator. `tornado.web.``removeslash`(*method*)[[source]](#) Use this decorator to remove trailing slashes from the request path. For example, a request to `/foo/` would redirect to `/foo` with thisdecorator. Your request handler mapping should use a regular expressionlike `r'/foo/*'` in conjunction with using the decorator. `tornado.web.``stream_request_body`(*cls*)[[source]](#) Apply to [`RequestHandler`](# "tornado.web.RequestHandler") subclasses to enable streaming body support. This decorator implies the following changes: - [`HTTPServerRequest.body`](# "tornado.httputil.HTTPServerRequest.body") is undefined, and body arguments will notbe included in [`RequestHandler.get_argument`](# "tornado.web.RequestHandler.get_argument"). - [`RequestHandler.prepare`](# "tornado.web.RequestHandler.prepare") is called when the request headers have beenread instead of after the entire body has been read. - The subclass must define a method `data_received(self, data):`, whichwill be called zero or more times as data is available. Note thatif the request has an empty body, `data_received` may not be called. - `prepare` and `data_received` may return Futures (such as via`@gen.coroutine`, in which case the next method will not be calleduntil those futures have completed. - The regular HTTP method (`post`, `put`, etc) will be called afterthe entire body has been read. There is a subtle interaction between `data_received` and asynchronous`prepare`: The first call to `data_received` may occur at any pointafter the call to `prepare` has returned *or yielded*. ### Everything else *exception *`tornado.web.``HTTPError`(*status_code=500*, *log_message=None*, **args*, ***kwargs*)[[source]](#) An exception that will turn into an HTTP error response. Raising an [`HTTPError`](# "tornado.web.HTTPError") is a convenient alternative to calling[`RequestHandler.send_error`](# "tornado.web.RequestHandler.send_error") since it automatically ends thecurrent function. To customize the response sent with an [`HTTPError`](# "tornado.web.HTTPError"), override[`RequestHandler.write_error`](# "tornado.web.RequestHandler.write_error"). <table class="docutils field-list" frame="void" rules="none"><col class="field-name"/><col class="field-body"/><tbody valign="top"><tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple"><li>status_code (<a class="reference external" href="https://docs.python.org/3.4/library/functions.html#int" title="(in Python v3.4)">int</a> [https://docs.python.org/3.4/library/functions.html#int]) – HTTP status code. Must be listed in<a class="reference external" href="https://docs.python.org/3.4/library/http.client.html#http.client.responses" title="(in Python v3.4)"><code class="xref py py-obj docutils literal">httplib.responses</code></a> [https://docs.python.org/3.4/library/http.client.html#http.client.responses] unless the <code class="docutils literal">reason</code>keyword argument is given.</li><li>log_message (<a class="reference external" href="https://docs.python.org/3.4/library/string.html#module-string" title="(in Python v3.4)">string</a> [https://docs.python.org/3.4/library/string.html#module-string]) – Message to be written to the log for this error(will not be shown to the user unless the <a class="reference internal" href="#tornado.web.Application" title="tornado.web.Application"><code class="xref py py-obj docutils literal">Application</code></a> is in debugmode). May contain <code class="docutils literal">%s</code>-style placeholders, which will be filledin with remaining positional parameters.</li><li>reason (<a class="reference external" href="https://docs.python.org/3.4/library/string.html#module-string" title="(in Python v3.4)">string</a> [https://docs.python.org/3.4/library/string.html#module-string]) – Keyword-only argument. The HTTP “reason” phraseto pass in the status line along with <code class="docutils literal">status_code</code>. Normallydetermined automatically from <code class="docutils literal">status_code</code>, but can be usedto use a non-standard numeric code.</li></ul></td></tr></tbody></table> *exception *`tornado.web.``Finish`[[source]](#) An exception that ends the request without producing an error response. When [`Finish`](# "tornado.web.Finish") is raised in a [`RequestHandler`](# "tornado.web.RequestHandler"), the request willend (calling [`RequestHandler.finish`](# "tornado.web.RequestHandler.finish") if it hasn't already beencalled), but the error-handling methods (including[`RequestHandler.write_error`](# "tornado.web.RequestHandler.write_error")) will not be called. If [`Finish()`](# "tornado.web.Finish") was created with no arguments, the pending responsewill be sent as-is. If [`Finish()`](# "tornado.web.Finish") was given an argument, thatargument will be passed to [`RequestHandler.finish()`](# "tornado.web.RequestHandler.finish"). This can be a more convenient way to implement custom error pagesthan overriding `write_error` (especially in library code): ~~~ if self.current_user is None: self.set_status(401) self.set_header('WWW-Authenticate', 'Basic realm="something"') raise Finish() ~~~ Changed in version 4.3: Arguments passed to `Finish()` will be passed on to[`RequestHandler.finish`](# "tornado.web.RequestHandler.finish"). *exception *`tornado.web.``MissingArgumentError`(*arg_name*)[[source]](#) Exception raised by [`RequestHandler.get_argument`](# "tornado.web.RequestHandler.get_argument"). This is a subclass of [`HTTPError`](# "tornado.web.HTTPError"), so if it is uncaught a 400 responsecode will be used instead of 500 (and a stack trace will not be logged). New in version 3.1. *class *`tornado.web.``UIModule`(*handler*)[[source]](#) A re-usable, modular UI unit on a page. UI modules often execute additional queries, and they can includeadditional CSS and JavaScript that will be included in the outputpage, which is automatically inserted on page render. Subclasses of UIModule must override the [`render`](# "tornado.web.UIModule.render") method. `render`(**args*, ***kwargs*)[[source]](#) Override in subclasses to return this module's output. `embedded_javascript`()[[source]](#) Override to return a JavaScript stringto be embedded in the page. `javascript_files`()[[source]](#) Override to return a list of JavaScript files needed by this module. If the return values are relative paths, they will be passed to[`RequestHandler.static_url`](# "tornado.web.RequestHandler.static_url"); otherwise they will be used as-is. `embedded_css`()[[source]](#) Override to return a CSS stringthat will be embedded in the page. `css_files`()[[source]](#) Override to returns a list of CSS files required by this module. If the return values are relative paths, they will be passed to[`RequestHandler.static_url`](# "tornado.web.RequestHandler.static_url"); otherwise they will be used as-is. `html_head`()[[source]](#) Override to return an HTML string that will be put in the <head/>element. `html_body`()[[source]](#) Override to return an HTML string that will be put at the end ofthe <body/> element. `render_string`(*path*, ***kwargs*)[[source]](#) Renders a template and returns it as a string. *class *`tornado.web.``ErrorHandler`(*application*, *request*, ***kwargs*)[[source]](#) Generates an error response with `status_code` for all requests. *class *`tornado.web.``FallbackHandler`(*application*, *request*, ***kwargs*)[[source]](#) A [`RequestHandler`](# "tornado.web.RequestHandler") that wraps another HTTP server callback. The fallback is a callable object that accepts an[`HTTPServerRequest`](# "tornado.httputil.HTTPServerRequest"), such as an [`Application`](# "tornado.web.Application") or[`tornado.wsgi.WSGIContainer`](# "tornado.wsgi.WSGIContainer"). This is most useful to use bothTornado `RequestHandlers` and WSGI in the same server. Typicalusage: ~~~ wsgi_app = tornado.wsgi.WSGIContainer( django.core.handlers.wsgi.WSGIHandler()) application = tornado.web.Application([ (r"/foo", FooHandler), (r".*", FallbackHandler, dict(fallback=wsgi_app), ]) ~~~ *class *`tornado.web.``RedirectHandler`(*application*, *request*, ***kwargs*)[[source]](#) Redirects the client to the given URL for all GET requests. You should provide the keyword argument `url` to the handler, e.g.: ~~~ application = web.Application([ (r"/oldpath", web.RedirectHandler, {"url": "/newpath"}), ]) ~~~ *class *`tornado.web.``StaticFileHandler`(*application*, *request*, ***kwargs*)[[source]](#) A simple handler that can serve static content from a directory. A [`StaticFileHandler`](# "tornado.web.StaticFileHandler") is configured automatically if you pass the`static_path` keyword argument to [`Application`](# "tornado.web.Application"). This handlercan be customized with the `static_url_prefix`, `static_handler_class`,and `static_handler_args` settings. To map an additional path to this handler for a static data directoryyou would add a line to your application like: ~~~ application = web.Application([ (r"/content/(.*)", web.StaticFileHandler, {"path": "/var/www"}), ]) ~~~ The handler constructor requires a `path` argument, which specifies thelocal root directory of the content to be served. Note that a capture group in the regex is required to parse the value forthe `path` argument to the get() method (different than the constructorargument above); see [`URLSpec`](# "tornado.web.URLSpec") for details. To serve a file like `index.html` automatically when a directory isrequested, set `static_handler_args=dict(default_filename="index.html")`in your application settings, or add `default_filename` as an initializerargument for your `StaticFileHandler`. To maximize the effectiveness of browser caching, this class supportsversioned urls (by default using the argument `?v=`). If a versionis given, we instruct the browser to cache this file indefinitely.[`make_static_url`](# "tornado.web.StaticFileHandler.make_static_url") (also available as [`RequestHandler.static_url`](# "tornado.web.RequestHandler.static_url")) canbe used to construct a versioned url. This handler is intended primarily for use in development and light-dutyfile serving; for heavy traffic it will be more efficient to usea dedicated static file server (such as nginx or Apache). We supportthe HTTP `Accept-Ranges` mechanism to return partial content (becausesome browsers require this functionality to be present to seek inHTML5 audio or video). **Subclassing notes** This class is designed to be extensible by subclassing, but becauseof the way static urls are generated with class methods rather thaninstance methods, the inheritance patterns are somewhat unusual.Be sure to use the `@classmethod` decorator when overriding aclass method. Instance methods may use the attributes `self.path``self.absolute_path`, and `self.modified`. Subclasses should only override methods discussed in this section;overriding other methods is error-prone. Overriding`StaticFileHandler.get` is particularly problematic due to thetight coupling with `compute_etag` and other methods. To change the way static urls are generated (e.g. to match the behaviorof another server or CDN), override [`make_static_url`](# "tornado.web.StaticFileHandler.make_static_url"), [`parse_url_path`](# "tornado.web.StaticFileHandler.parse_url_path"),[`get_cache_time`](# "tornado.web.StaticFileHandler.get_cache_time"), and/or [`get_version`](# "tornado.web.StaticFileHandler.get_version"). To replace all interaction with the filesystem (e.g. to servestatic content from a database), override [`get_content`](# "tornado.web.StaticFileHandler.get_content"),[`get_content_size`](# "tornado.web.StaticFileHandler.get_content_size"), [`get_modified_time`](# "tornado.web.StaticFileHandler.get_modified_time"), [`get_absolute_path`](# "tornado.web.StaticFileHandler.get_absolute_path"), and[`validate_absolute_path`](# "tornado.web.StaticFileHandler.validate_absolute_path"). Changed in version 3.1: Many of the methods for subclasses were added in Tornado 3.1. `compute_etag`()[[source]](#) Sets the `Etag` header based on static url version. This allows efficient `If-None-Match` checks against cachedversions, and sends the correct `Etag` for a partial response(i.e. the same `Etag` as the full file). New in version 3.1. `set_headers`()[[source]](#) Sets the content and caching headers on the response. New in version 3.1. `should_return_304`()[[source]](#) Returns True if the headers indicate that we should return 304. New in version 3.1. *classmethod *`get_absolute_path`(*root*, *path*)[[source]](#) Returns the absolute location of `path` relative to `root`. `root` is the path configured for this [`StaticFileHandler`](# "tornado.web.StaticFileHandler")(in most cases the `static_path`[`Application`](# "tornado.web.Application") setting). This class method may be overridden in subclasses. By defaultit returns a filesystem path, but other strings may be usedas long as they are unique and understood by the subclass'soverridden [`get_content`](# "tornado.web.StaticFileHandler.get_content"). New in version 3.1. `validate_absolute_path`(*root*, *absolute_path*)[[source]](#) Validate and return the absolute path. `root` is the configured path for the [`StaticFileHandler`](# "tornado.web.StaticFileHandler"),and `path` is the result of [`get_absolute_path`](# "tornado.web.StaticFileHandler.get_absolute_path") This is an instance method called during request processing,so it may raise [`HTTPError`](# "tornado.web.HTTPError") or use methods like[`RequestHandler.redirect`](# "tornado.web.RequestHandler.redirect") (return None after redirecting tohalt further processing). This is where 404 errors for missing filesare generated. This method may modify the path before returning it, but note thatany such modifications will not be understood by [`make_static_url`](# "tornado.web.StaticFileHandler.make_static_url"). In instance methods, this method's result is available as`self.absolute_path`. New in version 3.1. *classmethod *`get_content`(*abspath*, *start=None*, *end=None*)[[source]](#) Retrieve the content of the requested resource which is locatedat the given absolute path. This class method may be overridden by subclasses. Note that itssignature is different from other overridable class methods(no `settings` argument); this is deliberate to ensure that`abspath` is able to stand on its own as a cache key. This method should either return a byte string or an iteratorof byte strings. The latter is preferred for large filesas it helps reduce memory fragmentation. New in version 3.1. *classmethod *`get_content_version`(*abspath*)[[source]](#) Returns a version string for the resource at the given path. This class method may be overridden by subclasses. Thedefault implementation is a hash of the file's contents. New in version 3.1. `get_content_size`()[[source]](#) Retrieve the total size of the resource at the given path. This method may be overridden by subclasses. New in version 3.1. Changed in version 4.0: This method is now always called, instead of only whenpartial results are requested. `get_modified_time`()[[source]](#) Returns the time that `self.absolute_path` was last modified. May be overridden in subclasses. Should return a [`datetime`](https://docs.python.org/3.4/library/datetime.html#datetime.datetime "(in Python v3.4)") [https://docs.python.org/3.4/library/datetime.html#datetime.datetime]object or None. New in version 3.1. `get_content_type`()[[source]](#) Returns the `Content-Type` header to be used for this request. New in version 3.1. `set_extra_headers`(*path*)[[source]](#) For subclass to add extra headers to the response `get_cache_time`(*path*, *modified*, *mime_type*)[[source]](#) Override to customize cache control behavior. Return a positive number of seconds to make the resultcacheable for that amount of time or 0 to mark resource ascacheable for an unspecified amount of time (subject tobrowser heuristics). By default returns cache expiry of 10 years for resources requestedwith `v` argument. *classmethod *`make_static_url`(*settings*, *path*, *include_version=True*)[[source]](#) Constructs a versioned url for the given path. This method may be overridden in subclasses (but note that itis a class method rather than an instance method). Subclassesare only required to implement the signature`make_static_url(cls, settings, path)`; other keywordarguments may be passed through [`static_url`](# "tornado.web.RequestHandler.static_url")but are not standard. `settings` is the [`Application.settings`](# "tornado.web.Application.settings") dictionary. `path`is the static path being requested. The url returned should berelative to the current host. `include_version` determines whether the generated URL shouldinclude the query string containing the version hash of thefile corresponding to the given `path`. `parse_url_path`(*url_path*)[[source]](#) Converts a static URL path into a filesystem path. `url_path` is the path component of the URL with`static_url_prefix` removed. The return value should befilesystem path relative to `static_path`. This is the inverse of [`make_static_url`](# "tornado.web.StaticFileHandler.make_static_url"). *classmethod *`get_version`(*settings*, *path*)[[source]](#) Generate the version string to be used in static URLs. `settings` is the [`Application.settings`](# "tornado.web.Application.settings") dictionary and `path`is the relative location of the requested asset on the filesystem.The returned value should be a string, or `None` if no versioncould be determined. Changed in version 3.1: This method was previously recommended for subclasses to override;[`get_content_version`](# "tornado.web.StaticFileHandler.get_content_version") is now preferred as it allows the baseclass to handle caching of the result. © Copyright 2009-2016, The Tornado Authors. Created using [Sphinx](http://sphinx-doc.org/) 1.3.5.