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:
Responding to unpublished requests
Logging and notifying users appropriately when unhandled exceptions occur
The difference between query strings and POSTed params
The decoding and unpacking of request headers and bodies, including file uploads
Response status or headers
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, .headerMap, and/or
.body.
The design of HTTP itself is guided by REST, a set of principles which constrain its expressivity and therefore its implementation. HTTP is a transfer protocol which enables the exchange of representations of resources. In a RESTful design, clients never expect to access a resource directly; instead, they request a representation of that resource. For example, if a resource has both an XML and an HTML representation, then an HTTP/1.1 server might be expected to inspect the Accept request header in order to decide which representation to serve in response.
It's important to clarify some terminology, here. In REST terms, a "resource" is "any concept that might be the target of an author’s hypertext reference...a conceptual mapping to a set of entities, not the entity that corresponds to the mapping at any particular point in time". A resource is not the request, nor the response, in an HTTP conversation. "The resource is not the storage object. The resource is not a mechanism that the server uses to handle the storage object. The resource is a conceptual mapping — the server receives the identifier (which identifies the mapping) and applies it to its current mapping implementation (usually a combination of collection-specific deep tree traversal and/or hash tables) to find the currently responsible handler implementation and the handler implementation then selects the appropriate action+response based on the request content."
CherryPy, therefore, does not provide REST resources, nor model them, nor serve them. Instead, it provides mappings between identifiers (URI's) and handlers (functions). It allows application developers to model resources, perhaps, but it only serves representations of resources.
By default, these identifier-to-handler mappings (which we will call "handler dispatch" from now on) follow a simple pattern: since the path portion of a URI is hierarchical, CherryPy arranges handlers in a similar heirarchy, starting at cherrypy.root, and branching on each attribute; every leaf node in this tree must be "exposed" (but the branches need not be, see section 2.2). Note in particular that, although the query portion of a Request-URI is part of the resource identifier, CherryPy does not use it to map identifiers to handlers. Application developers may use the query string to further identify the requested resource, of course, but CherryPy, not having any domain-specific knowledge about the format or semantic of a query string, doesn't try to guess.
Filters, then, are CherryPy's way to wrap or circumvent the default handler dispatch. EncodingFilter, for example, wraps the response from a handler, encoding the response body as it is produced. StaticFilter, on the other hand, intercepts some requests (based on the path portion of the Request-URI) and implements its own identifier-to-handler mapping. Developers who wish to provide their own handler dispatch mechanisms are encouraged to do so via a filter.
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 headerMap 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.paramMap; 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 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.headerMap['Host'].
This attribute is a string containing the URL the client requested. By default, it
is equal to request.base + request.path.
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.paramMap, in case it is modified by a filter during the request.
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 headers. In general, you should use request.headerMap 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 initOnly 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 serverClass 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):
cherrypy._cphttpserver.CherryHTTPServer: this will load the old, single-threaded built-in HTTP server. This server is deprecated and will probably be removed in CherryPy 2.2.cherrypy._cphttpserver.PooledThreadServer: this will load the old, multi-threaded built-in HTTP server. This server is deprecated and will probably be removed in CherryPy 2.2.cherrypy._cphttpserver.embedded_server: use this to automatically select between the CherryHTTPServer and the PooledThreadServer based on the value of config.get("server.threadPool") and config.get("server.socketFile").None: this will not load any HTTP server. Note that this is not the default; the default (if serverClass is not given) is to load the WSGIServer.Any other class (or dotted-name string): load a custom HTTP server.
You must call this function from Python's main thread, and set initOnly 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 "initOnly" 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:
STOPPED = 0: The server hasn't been started, and will not accept requests.
STARTING = None: The server is in the process of starting, or an error occured while trying to start the server.
STARTED = 1: The server has started (including an HTTP server if requested), and is ready to receive requests.
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.
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 onStartThreadList functions upon the first request using each distinct thread.
A list of functions that will be called when each request thread is stopped.
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.
This exception can be used to automatically send a response using a http status code, with an appropriate error page.
Utility class that exposes a getitem-aware object. It does not provide index() or default() methods, and it does not expose the individual item objects - just the list or dict that contains them. User-specific index() and default() methods can be implemented by inheriting from this class.
Utility class that restores positional parameters functionality that was found in 2.0.0-beta.
Returns a list of (start, stop) indices from a Range request header. Returns None if no such header is provided in the request. Each (start, stop) tuple will be composed of two ints, which are suitable for use in a slicing operation. That is, the header "Range: bytes=3-6", if applied against a Python string, is requesting resource[3:7]. This function will return the list [(3, 7)].
Set status, headers, and body in order to serve the file at the given path. The Content-Type header will be set to the contentType arg, if provided. If not provided, the Content-Type will be guessed by the extension of the file. If disposition is not None, the Content-Disposition header will be set to "<disposition>; filename=<name>". If name is None, it will be set to the basename of path. If disposition is None, no Content-Disposition header will be written.
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:
Example 3.7. Profiling example
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:
_cpOnError is a function for handling unanticipated exceptions, whether raised by CherryPy itself, or in user applications. The default simply raises HTTPError(500).
Filters provide a powerful mechanism for extending CherryPy. The aim is to provide code called at the HTTP request level itself. More specifically it means that you can write code that will be called:
- before a request is processed
- after a request has been processed
- before a response is sent to the client
- after a response is sent to the client
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
- baseUrlFilter.baseUrl
- baseUrlFilter.useXForwardedHost
The decoding filter can be configured to automatically decode incoming requests.
The decodingfilter has the following configuration options:
- decodingFilter.encoding
The encodingfilter can be configured to automatically encode outgoing responses.
The encodingfilter has the following configuration options:
- encodingFilter.encoding
- encodingFilter.mimeTypeList
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 static filter allows CherryPy to serve static files.
The staticfilter has the following configuration options:
- staticFilter.file
- staticFilter.dir
staticFilter.root
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:
- tidyFilter.tmpDir
- tidyFilter.strictXml, False
- tidyFilter.tidyPath
- encodingFilter.errorsToIgnore, []
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:
- virtualHostFilter.prefix, '/'
The xmlrpcfilter converts XMLRPC to the CherryPy2 object system and vice-versa.
PLEASE NOTE: beforeRequestBody: 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. beforeFinalize: 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.
CherryPy 2.1 supports arbitrary WSGI servers, and includes its own WSGI server (the default). This means that you should be able to deploy your CherryPy application using Apache or IIS (among others) without any changes to your application--only the deployment scripts will change.