The CherryPy Documentation

There are some special cases, however. To what handler should we map a path like "/admin/search/"? Note the trailing slash after "search"—it indicates that our path has three components: "admin", "search", and "". Static webservers interpret this to mean that the search object is a directory, and, since the third component is blank, they use an index.html file if it exists. CherryPy is a dynamic webserver, so it allows you to specify an index method to handle this. In our example, CherryPy will look for a handler at cherrypy.root.admin.search.index. Let's pause and show our example application so far:

import cherrypy

class Root:
    def index(self):
        return "Hello, world!"
    index.exposed = True

class Admin:
    def user(self, name=""):
        return "You asked for user '%s'" % name
    user.exposed = True

class Search:
    def index(self):
        return search_page()
    index.exposed = True

cherrypy.root = Root()
cherrypy.root.admin = Admin()
cherrypy.root.admin.search = Search()

So far, we have three exposed handlers:

Yes, you read that third line correctly: root.admin.search.index will be called whether or not the URI has a trailing slash. Actually, that isn't quite true; CherryPy will answer a request for "/admin/search" (without the slash) with an HTTP Redirect response. Most browsers will then request "/admin/search/" as the redirection suggests, and then our root.admin.search.index handler will be called. But the final outcome is the same.

Now, let's consider another special case. What if, instead of passing a user name as a parameter, we wish to use a user id as part of the path? What to do with a URI like "/admin/user/8173/schedule"? This is intended to reference the schedule belonging to "user #8173", but we certainly don't want to have a separate function for each user id!

CherryPy allows you to map a single handler to multiple URI's with the simple approach of not writing handlers you don't need. If a node in the cherrypy.root tree doesn't have any children, that node will be called for all of its child paths, and CherryPy will pass the leftover path info as positional arguments. In our example, CherryPy will call cherrypy.root.admin.user("8173", "schedule"). Let's rewrite our user method to handle such requests:

class Admin:
    def user(self, *args):
        if not args:
            raise cherrypy.HTTPError(400, "A user id was expected but not supplied.")
        id = args.pop(0)
        if args and args[0] == 'schedule':
            return self.schedule(id)
        return "You asked for user '%s'" % id
    user.exposed = True

Note that this is different behavior than CherryPy 2.1, which only allowed positional params for methods named "default".

Are you ready for another special case? What handler is called in our example if you request the URI "/not/a/valid/path"? Given the behavior we have described up to this point, you might deduce that the root.index method will end up handling any path that can't be mapped elsewhere. This would mean, in effect, that CherryPy applications with a root.index could never return a "404 Not Found" response!

To prevent this, CherryPy doesn't try to call index methods unless they are attached to the last node in the path; in our example, the only index method that might be called would be a root.not.a.valid.path.index method. If you truly want an intermediate index method to receive positional parameters, well, you can't do that. But what you can do is define a default method to do that for you, instead of an index method. If we wanted our cherrypy.root to handle any child path, and receive positional parameters, we could rewrite it like this:

class Root:
    def index(self):
        return "Hello, world!"
    index.exposed = True
    
    def default(self, *args):
        return "Extra path info: %s" % repr(args)
    default.exposed = True

This new Root class would handle the URI's "/" and "/index" via the index method, and would handle URI's like "/not/a/valid/path" and "/admin/unknown" via the default method.

For those of you who need to see in exactly what order CherryPy will try various handlers, here are some examples, using the application above. We always start by trying to find the longest object path first, and then working backwards until an exposed, callable handler is found:

"/admin/user/8192/schedule"
    Trying to reach cherrypy.root.admin.user.8192.schedule.index...
    cherrypy.root                     exists? Yes.
            .root.admin               exists? Yes.
                 .admin.user          exists? Yes.
                       .user.8192     exists? No.
                       .user.default  is callable and exposed? No.
                 .admin.user          is callable and exposed? Yes. Call it.

"/admin/search/"
    Trying to reach cherrypy.root.admin.search.index...
    cherrypy.root                     exists? Yes.
            .root.admin               exists? Yes.
                 .admin.search        exists? Yes.
                       .search.index  exists? Yes. Path exhausted.
                       .search.index  is callable and exposed? Yes. Call it.

"/admin/unknown"
    Trying to reach cherrypy.root.admin.unknown.index...
    cherrypy.root                     exists? Yes.
            .root.admin               exists? Yes.
                 .admin.unknown       exists? No.
                 .admin.default       is callable and exposed? No.
            .root.admin               is callable and exposed? No.
            .root.default             is callable and exposed? Yes. Call it.

The server.environment entry controls how CherryPy should run. Three values are built in:

Beginning in CherryPy 2.2, the behavior of each environment is defined in cherrypy.config.environments, a dict whose keys are "development", "production", etc, and whose values are dicts of config keys and values. Application developers are free to modify existing environments, or define new environments for use by their deployers, by modifying this container. For example, if you develop an application which absolutely cannot handle autoreload, your app can set cherrypy.config.environments['development']['autoreload.on'] = False. Deployers who selected the "development" environment would then be free from the danger of autoreload interacting with your application. Another example of using config.environments directly might be an application which needs a "development" and "production" environment, but also separate "beta", "rc", "live data" and/or "testing" environments.

At its most basic, CherryPy is designed to allow the production of simple websites without having to think about any of the details of HTTP. Notice we're saying HTTP (the transport), not HTML (the markup language)! In particular, developers should not have to concern themselves with:

For the most part, simple "page handlers" (functions attached to cherrypy.root), should never have to refer to cherrypy at all! They receive params via function arguments, and return content directly. Advanced functionality is most often enabled via the built-in filters, which encapsulate the particulars of HTTP, and can be completely controlled via the config file.

Simple apps are produced simply, but when a developer needs to step out of the mundane and provide real value, they should be able to leverage the complete power and flexibility of the HTTP specification. In general, the HTTP request and response messages are completely represented in the cherrypy.request and .response objects. At the lowest level, a developer should be able to generate any valid HTTP response message by modifying cherrypy.response.status, .headers, and/or .body.

This attribute is a string containing the IP address of the client. It will be an empty string if it is not available.

This attribute is an int containing the TCP port number of the client. It will be -1 if it is not available.

This attribute is a string containing the remote hostname of the client.

This attribute is a dictionary containing the received HTTP headers, with automatically titled keys (e.g., "Content-Type"). As it's a dictionary, no duplicates are allowed.

This attribute is a list of (header, value) tuples containing the received HTTP headers. In general, you probably want to use headers instead; this is only here in case you need to inspect duplicates in the request headers.

This attribute is a string containing the first line of the raw HTTP request; for example, "GET /path/page HTTP/1.1".

This attribute is a SimpleCookie instance from the standard library's Cookie module which contains the incoming cookie values from the client.

This attribute is the input stream to the client, if applicable. See cherrypy.request.processRequestBody for more information.

This attribute is the request entity body, if applicable. See cherrypy.request.processRequestBody for more information.

This attribute specifies whether or not the request's body (request.rfile, which is POST or PUT data) will be handled by CherryPy. If True (the default for POST and PUT requests), then request.rfile will be consumed by CherryPy (and unreadable after that). If the request Content-Type is "application/x-www-form-urlencoded", then the rfile will be parsed and placed into request.params; otherwise, it will be available in request.body. If cherrypy.request.processRequestBody is False, then the rfile is not consumed, but will be readable by the exposed method.

This attribute is a string containing the HTTP request method, such as GET or POST.

This attribute is a string containing the HTTP protocol of the request in the form of HTTP/x.x

This attribute is a Version object which represents the HTTP protocol. It's the same os request.protocol, but allows easy comparisons like if cherrypy.request.version >= "1.1": do_http_1_1_thing.

This attribute is a dictionary containing the WSGI environment for the request. In non-WSGI settings (i.e., custom HTTP servers), it is absent.

This attribute is a string containing the query string of the request (the part of the URL following '?').

This attribute is a string containing the path of the resource the client requested.

This attribute is a dictionary containing the query string and POST arguments of this request.

This attribute is a string containing the root URL of the server. By default, it is equal to request.scheme://request.headers['Host'].

This attribute is a string containing the URL the client requested. By default, it is equal to request.base + request.path, plus the querystring, if provided.

This attribute is a string containing the path of the exposed method that will be called to handle this request. This is usually the same as cherrypy.request.path, but can be changed in a filter to change which method is actually called.

This attribute is a string containing the original value of cherrypy.request.path, in case it is modified by a filter during the request.

This attribute is a string containing the original value of cherrypy.request.params, in case it is modified by a filter during the request.

This attribute is a string containing the URL scheme used in this request. It is either "http" or "https".

This attribute is a dictionary with automatically titled keys (e.g., "Content-Length"). It holds all outgoing HTTP headers to the client.

This attribute is a list of (header, value) tuples. It's not available until the response has been finalized; it's really only there in the extremely rare cases when you need duplicate response header_list. In general, you should use request.headers instead.

This attribute is a SimpleCookie instance from the standard library's Cookie module. It contains the outgoing cookie values.

This attribute is originally just the return value of the exposed method, but by the end of the request it must be an iterable (usually a list or generator of strings) which will be the content of the HTTP response.

This attribute is a string containing the HTTP response code in the form "### Reason-Phrase", i.e. "200 OK". You may also set it to an int, in which case the response finalization process will supply a Reason-Phrase for you.

This attribute is a Version object, representing the HTTP protocol version of the response. This is not necessarily the value that will be written in the response! Instead, it should be used to determine which features are available for the response. For example, an HTTP server may send an HTTP/1.1 response even though the client is known to only understand HTTP/1.0—the response.version will be set to Version("1.0") to inform you of this, so that you (and CherryPy) can restrict the response to HTTP/1.0 features only.

Start the CherryPy Server. Simple websites may call this without any arguments, to run the default server. If init_only is False (the default), this function will block until KeyboardInterrupt or SystemExit is raised, so that the process will persist. When using one of the built-in HTTP servers, you should leave this set to False. You should only set it to True if you're running CherryPy as an extension to another HTTP server (for example, when using Apache and mod_python with CherryPy), in which case the foreign HTTP server should do its own process-management.

Use the server_class argument to specify that you wish to use an HTTP server other than the default, built-in WSGIServer. If missing, config.get("server.class") will be checked for an alternate value; otherwise, the default is used. Possible alternate values (you may pass the class names as a string if you wish):

You must call this function from Python's main thread, and set init_only to False, if you want CherryPy to shut down when KeyboardInterrupt or SystemExit are raised (including Ctrl-C). The only time you might want to do otherwise is if you run CherryPy as a Windows service, or as an extension to, say, mod_python, and even then, you might want to anyway.

If the "init_only" argument to server.start is True, this will be False, and vice-versa.

Whatever HTTP server class is set in server.start will be stuck in here.

Whatever HTTP server class is set in server.start will be instantiated and stuck in here.

One of three values, indicating the state of the server:

True if the server is ready to receive requests, false otherwise. Read-only.

Since server.start usually blocks, other threads need to be started before calling server.start; however, they often must wait for server.start to complete it's setup of the HTTP server. Use this function from other threads to make them wait for the HTTP server to be ready to receive requests.

Since server.start usually blocks, use this to easily run another function in a new thread. It starts the new thread and then runs server.start. The new thread automatically waits for the server to finish its startup procedure.

Stop the CherryPy Server. Well, "suspend" might be a better term—this doesn't terminate the process.

Usually None, set this to KeyboardInterrupt() or SystemExit() to shut down the entire process. That is, the new exception will be raised in the main thread.

Restart the CherryPy Server.

A list of functions that will be called when the server starts.

A list of functions that will be called when the server stops.

A list of functions that will be called when each request thread is started. Note that such threads do not need to be started or controlled by CherryPy; for example, when using CherryPy with mod_python, Apache will start and stop the request threads. Nevertheless, CherryPy will run the on_start_thread_list functions upon the first request using each distinct thread.

A list of functions that will be called when each request thread is stopped.

HTTP servers should call this function to create a new Request and Response object. The return value is the Request object; call its run method to have the CherryPy core process the request data and populate the response.

This function returns the configuration value for the given key. The function checks if the setting is defined for the current request path; it walks up the request path until the key is found, or it returns the default value. If returnSection is True, the function returns the configuration path where the key is defined instead.

The getAll function returns a list containing a (path, value) tuple for all occurences of the key within the request path. This function allows applications to inherit configuration data defined for parent paths.

Function to update the configuration map. The "updateMap" argument is a dictionary of the form {'sectionPath' : { } }. The "file" argument is the path to the configuration file.

Dict containing config defaults for each named server.environment.

Function to mount a tree of objects at the given baseurl, using the given configuration dict or filename. If baseurl is None or missing, it is assumed to be "/" unless the config specifies [global] mount_point = "/path/to/approot". If conf is not None, then each of its sections (which should be a relative URL, like "/skins/deepblue/main") will be prefixed with the baseurl, so that config lookups are also "mounted" at the base URL.

Note that, by using tree.mount, your approot may not be found at cherrypy.root; there may be several "dummy" objects placed in-between cherrypy.root and your application's root instance.

A dict of the form {baseurl: approot-instance}.

A method which finds the appropriate baseurl for a given path. If path is None or missing, cherrypy.request.object_path is used. If multiple applications "contain" the given path, the longer baseurl is returned. That is, if App1 is mounted at "/" and App2 is mounted at "/path/to/app", then cherrypy.tree.mount_point("/path/to/app/main") will return "/path/to/app".

Once you have obtained the baseurl using mount_point, you can obtain a reference to the application root object by looking up cherrypy.tree.mount_points[baseurl].

Prefixes the given path with the given mount_point, which isn't very exciting unless mount_point is None or missing, in which case, cherrypy.request.object_path will be used to find the current mount_point and prefix that to the given path.

This exception can be used to automatically send a response using a http status code, with an appropriate error page.

This exception will force a HTTP redirect.

This exception will redirect processing to another path within the site (without informing the client). Provide the new path as an argument when raising the exception. You may also provide a second "params" argument which will replace the current request params (usually a dict, but you may also supply a GET-param-style string). This exception is only handled from within page handlers and before_main filter methods.

This module both provides code-coverage tools, and may also be run as a script. To use this module, or the coverage tools in the test suite, you need to download 'coverage.py', either Gareth Rees' original implementation or Ned Batchelder's enhanced version.

Set cherrypy.codecoverage to True to turn on coverage tracing. Then, use the covercp.serve() function to browse the results in a web browser. If you run this module as a script (i.e., from the command line), it will call serve() for you.

You can profile any of your page handlers (exposed methods) as follows:

from cherrypy.lib import profile

class Root:
    p = profile.Profiler("/path/to/profile/dir")
    
    def index(self):
        self.p.run(self._index)
    index.exposed = True
    
    def _index(self):
        return "Hello, world!"

cherrypy.root = Root()

Set the config entry: "profiling.on = True" if you'd rather turn on profiling for all requests. Then, use the serve() function to browse the results in a web browser. If you run this module as a script (i.e., from the command line), it will call serve() for you.

Developers: this module should be used whenever you make significant changes to CherryPy, to get a quick sanity-check on the performance of the request process. Basic requests should complete in about 5 milliseconds on a reasonably-fast machine running Python 2.4 (Python 2.3 will be much slower due to threadlocal being implemented in Python, not C). You can profile the test suite by supplying the --profile option to test.py.

This module provides a brute-force method of reloading application files on the fly. When the config entry "autoreload.on" is True (or when "server.environment" is "development"), CherryPy uses the autoreload module to restart the current process whenever one of the files in use is changed. The mechanism by which it does so is pretty complicated:

Figure 3.3. The autoreload process

_cp_on_error is a function for handling unanticipated exceptions, whether raised by CherryPy itself, or in user applications. The default simply responds as if HTTPError(500) had been raised.

_cp_on_http_error handles HTTPError responses, setting cherrypy.response.status, headers, and body.

User defined filters are enabled using the class attribute _cp_filters. Any filter instances placed in _cp_filters will be applied to all methods of the class.

Function to log HTTP requests into the access.log file.

Function to log errors into the error.log file. The cherrypy.log function is syntactic sugar for this one.

This hook is being called righ at the beginning of the request process. The only work CherryPy has done when this hook is called is to parse the first line of the HTTP request. This is needed so that filters have access to the object path translated from the path specified in the HTTP request.

This hook is always called.

This hook is being called right after CherryPy has parse the HTTP request headers but before it tries to parse the request body. If a filter which implements that hook sets cherrypy.request.processRequestBody to False, CherryPy will not parse the request body at all. This can be handy when you know your user agent returns the data in a form that the default CherryPy request body parsing function cannot understand.

For example, assuming your user agent returns you a request body which is an XML string unquoted, you may want a filter to parse that XML string and generates an XML DOM instance. Then the filter could add that instance to the cherrypy.request.params which in turns would be passed to your page handler like if it had actually been sent like that through the HTTP request. Therefore your filter has turned the XML string into an XML DOM instance transparently and makes your life easier. In that case you do not want CherryPy to parse the request body. It could also be used to scan the request body before it is being processed any further and decide to reject it if needed.

This hook is not called if an error occurs during the process before hand.

This hook is called right before your page handler (exposed callable) is being called by CherryPy. It can be handy if considering HTTP request headers or body you may want not to call the page handler at all, then you would have to set cherrypy.request.executeMain to False.

This hook is not called if an error occurs during the process before hand.

This hook is called right after the page handler has been processed (depending on the before_main hook behavior) and before CherryPy formats the final respone object. It helps you for example to check for what could have been returned by your page handler and change some headers of needed.

This hook is not called if an error occurs during the process before hand.

This hook is called at the end of the process so that you can finely tweak your HTTP response if needed (eg adding headers to the cherrypy.response.header_list). Note that cherrypy.response.headers will not be processed any longer at that stage.

This hook is always called.

This hook is called when an error has occured during the request processing. It allows you to called code before the _cp_on_error handler is being called as well as the response finalizing stage.

This hook is called when an error has occured during the request processing. It allows you to call code after the _cp_on_error handler is being called as well as the response finalizing stage.

The baseurlfilter changes the base url of a request. It is useful for running CherryPy behind Apache with mod_rewrite.

The baseurlfilter has the following configuration options

The cachefilter stores responses in memory. If an identical request is subsequently made, then the cached response is output without calling the page handler.

The decoding filter can be configured to automatically decode incoming requests.

The decodingfilter has the following configuration options:

The encodingfilter can be configured to automatically encode outgoing responses.

The encodingfilter has the following configuration options:

The gzipfilter will automatically gzip outgoing requests, if it is supported by the client.

The gzipfilter does not have any configuration options.

The logdebuinfofilter adds debug information to each page. The filter is automatically turned on when "server.environment" is set to "development".

The logdebuginfofilter has the following configuration options:

The nsgmlsfilter parses and validates SGML responses.

The sessionauthenticatefilter provides simple form-based authentication and access control.

The Session Filter has its own section

The static filter allows CherryPy to serve static files.

The staticfilter has the following configuration options:

The tidyfilter cleans up returned html by running the response through Tidy.

Note that we use the standalone Tidy tool rather than the python mxTidy module. This is because this module doesn't seem to be stable and it crashes on some HTML pages (which means that the server would also crash.)

The tidyfilter has the following configuration options:

The virtualhostfilter changes the ObjectPath based on the Host. Use this filter when running multiple sites within one CP server.

The virtualhostfilter has the following configuration options:

The wsgiappfilter allows the application developer or deployer to mount WSGI-compatible applications and middleware to locations on the CherryPy object tree.

Applications can be added to the tree by using the cherrypy.lib.cptools.WSGIApp convenience class to directly mount applications to the CherryPy tree. You can also add an instance of the filter to a class's _cp_filters list.

The cherrypy.lib.cptools.WSGIApp and WSGIAppFilter class contsructors takes the following parameters:

The xmlrpcfilter converts XMLRPC to the CherryPy2 object system and vice-versa.

PLEASE NOTE: before_request_body: Unmarshalls the posted data to a methodname and parameters. - These are stored in cherrypy.request.rpcMethod and .rpcParams - The method is also stored in cherrypy.request.path, so CP2 will find the right method to call for you, based on the root's position. before_finalize: Marshalls cherrypy.response.body to xmlrpc. - Until resolved: cherrypy.response.body must be a python source string; this string is 'eval'ed to return the results. This will be resolved in the future. - Content-Type and Content-Length are set according to the new (marshalled) data

The xmlrpcfilter does not have any configuration options.