21.6. "urllib.request" — Extensible library for opening URLs
************************************************************

**Source code:** Lib/urllib/request.py

======================================================================

The "urllib.request" module defines functions and classes which help
in opening URLs (mostly HTTP) in a complex world — basic and digest
authentication, redirections, cookies and more.

See also: The Requests package is recommended for a higher-level
  HTTP client interface.

The "urllib.request" module defines the following functions:

urllib.request.urlopen(url, data=None[, timeout], *, cafile=None, capath=None, cadefault=False, context=None)

   Open the URL *url*, which can be either a string or a "Request"
   object.

   *data* must be an object specifying additional data to be sent to
   the server, or "None" if no such data is needed.  See "Request" for
   details.

   urllib.request module uses HTTP/1.1 and includes "Connection:close"
   header in its HTTP requests.

   The optional *timeout* parameter specifies a timeout in seconds for
   blocking operations like the connection attempt (if not specified,
   the global default timeout setting will be used).  This actually
   only works for HTTP, HTTPS and FTP connections.

   If *context* is specified, it must be a "ssl.SSLContext" instance
   describing the various SSL options. See "HTTPSConnection" for more
   details.

   The optional *cafile* and *capath* parameters specify a set of
   trusted CA certificates for HTTPS requests.  *cafile* should point
   to a single file containing a bundle of CA certificates, whereas
   *capath* should point to a directory of hashed certificate files.
   More information can be found in
   "ssl.SSLContext.load_verify_locations()".

   The *cadefault* parameter is ignored.

   This function always returns an object which can work as a *context
   manager* and has methods such as

   * "geturl()" — return the URL of the resource retrieved, commonly
     used to determine if a redirect was followed

   * "info()" — return the meta-information of the page, such as
     headers, in the form of an "email.message_from_string()" instance
     (see Quick Reference to HTTP Headers)

   * "getcode()" – return the HTTP status code of the response.

   For HTTP and HTTPS URLs, this function returns a
   "http.client.HTTPResponse" object slightly modified. In addition to
   the three new methods above, the msg attribute contains the same
   information as the "reason" attribute — the reason phrase returned
   by server — instead of the response headers as it is specified in
   the documentation for "HTTPResponse".

   For FTP, file, and data URLs and requests explicitly handled by
   legacy "URLopener" and "FancyURLopener" classes, this function
   returns a "urllib.response.addinfourl" object.

   Raises "URLError" on protocol errors.

   Note that "None" may be returned if no handler handles the request
   (though the default installed global "OpenerDirector" uses
   "UnknownHandler" to ensure this never happens).

   In addition, if proxy settings are detected (for example, when a
   "*_proxy" environment variable like "http_proxy" is set),
   "ProxyHandler" is default installed and makes sure the requests are
   handled through the proxy.

   The legacy "urllib.urlopen" function from Python 2.6 and earlier
   has been discontinued; "urllib.request.urlopen()" corresponds to
   the old "urllib2.urlopen".  Proxy handling, which was done by
   passing a dictionary parameter to "urllib.urlopen", can be obtained
   by using "ProxyHandler" objects.

   Changed in version 3.2: *cafile* and *capath* were added.

   Changed in version 3.2: HTTPS virtual hosts are now supported if
   possible (that is, if "ssl.HAS_SNI" is true).

   New in version 3.2: *data* can be an iterable object.

   Changed in version 3.3: *cadefault* was added.

   Changed in version 3.4.3: *context* was added.

   Deprecated since version 3.6: *cafile*, *capath* and *cadefault*
   are deprecated in favor of *context*. Please use
   "ssl.SSLContext.load_cert_chain()" instead, or let
   "ssl.create_default_context()" select the system’s trusted CA
   certificates for you.

urllib.request.install_opener(opener)

   Install an "OpenerDirector" instance as the default global opener.
   Installing an opener is only necessary if you want urlopen to use
   that opener; otherwise, simply call "OpenerDirector.open()" instead
   of "urlopen()".  The code does not check for a real
   "OpenerDirector", and any class with the appropriate interface will
   work.

urllib.request.build_opener([handler, ...])

   Return an "OpenerDirector" instance, which chains the handlers in
   the order given. *handler*s can be either instances of
   "BaseHandler", or subclasses of "BaseHandler" (in which case it
   must be possible to call the constructor without any parameters).
   Instances of the following classes will be in front of the
   *handler*s, unless the *handler*s contain them, instances of them
   or subclasses of them: "ProxyHandler" (if proxy settings are
   detected), "UnknownHandler", "HTTPHandler",
   "HTTPDefaultErrorHandler", "HTTPRedirectHandler", "FTPHandler",
   "FileHandler", "HTTPErrorProcessor".

   If the Python installation has SSL support (i.e., if the "ssl"
   module can be imported), "HTTPSHandler" will also be added.

   A "BaseHandler" subclass may also change its "handler_order"
   attribute to modify its position in the handlers list.

urllib.request.pathname2url(path)

   Convert the pathname *path* from the local syntax for a path to the
   form used in the path component of a URL.  This does not produce a
   complete URL.  The return value will already be quoted using the
   "quote()" function.

urllib.request.url2pathname(path)

   Convert the path component *path* from a percent-encoded URL to the
   local syntax for a path.  This does not accept a complete URL.
   This function uses "unquote()" to decode *path*.

urllib.request.getproxies()

   This helper function returns a dictionary of scheme to proxy server
   URL mappings. It scans the environment for variables named
   "<scheme>_proxy", in a case insensitive approach, for all operating
   systems first, and when it cannot find it, looks for proxy
   information from Mac OSX System Configuration for Mac OS X and
   Windows Systems Registry for Windows. If both lowercase and
   uppercase environment variables exist (and disagree), lowercase is
   preferred.

   Note: If the environment variable "REQUEST_METHOD" is set, which
     usually indicates your script is running in a CGI environment,
     the environment variable "HTTP_PROXY" (uppercase "_PROXY") will
     be ignored. This is because that variable can be injected by a
     client using the “Proxy:” HTTP header. If you need to use an HTTP
     proxy in a CGI environment, either use "ProxyHandler" explicitly,
     or make sure the variable name is in lowercase (or at least the
     "_proxy" suffix).

The following classes are provided:

class urllib.request.Request(url, data=None, headers={}, origin_req_host=None, unverifiable=False, method=None)

   This class is an abstraction of a URL request.

   *url* should be a string containing a valid URL.

   *data* must be an object specifying additional data to send to the
   server, or "None" if no such data is needed.  Currently HTTP
   requests are the only ones that use *data*.  The supported object
   types include bytes, file-like objects, and iterables.  If no
   "Content-Length" nor "Transfer-Encoding" header field has been
   provided, "HTTPHandler" will set these headers according to the
   type of *data*.  "Content-Length" will be used to send bytes
   objects, while "Transfer-Encoding: chunked" as specified in **RFC
   7230**, Section 3.3.1 will be used to send files and other
   iterables.

   For an HTTP POST request method, *data* should be a buffer in the
   standard *application/x-www-form-urlencoded* format.  The
   "urllib.parse.urlencode()" function takes a mapping or sequence of
   2-tuples and returns an ASCII string in this format. It should be
   encoded to bytes before being used as the *data* parameter.

   *headers* should be a dictionary, and will be treated as if
   "add_header()" was called with each key and value as arguments.
   This is often used to “spoof” the "User-Agent" header value, which
   is used by a browser to identify itself – some HTTP servers only
   allow requests coming from common browsers as opposed to scripts.
   For example, Mozilla Firefox may identify itself as ""Mozilla/5.0
   (X11; U; Linux i686) Gecko/20071127 Firefox/2.0.0.11"", while
   "urllib"’s default user agent string is ""Python-urllib/2.6"" (on
   Python 2.6).

   An appropriate "Content-Type" header should be included if the
   *data* argument is present.  If this header has not been provided
   and *data* is not None, "Content-Type: application/x-www-form-
   urlencoded" will be added as a default.

   The final two arguments are only of interest for correct handling
   of third-party HTTP cookies:

   *origin_req_host* should be the request-host of the origin
   transaction, as defined by **RFC 2965**.  It defaults to
   "http.cookiejar.request_host(self)".  This is the host name or IP
   address of the original request that was initiated by the user. For
   example, if the request is for an image in an HTML document, this
   should be the request-host of the request for the page containing
   the image.

   *unverifiable* should indicate whether the request is unverifiable,
   as defined by **RFC 2965**.  It defaults to "False".  An
   unverifiable request is one whose URL the user did not have the
   option to approve.  For example, if the request is for an image in
   an HTML document, and the user had no option to approve the
   automatic fetching of the image, this should be true.

   *method* should be a string that indicates the HTTP request method
   that will be used (e.g. "'HEAD'").  If provided, its value is
   stored in the "method" attribute and is used by "get_method()". The
   default is "'GET'" if *data* is "None" or "'POST'" otherwise.
   Subclasses may indicate a different default method by setting the
   "method" attribute in the class itself.

   Note: The request will not work as expected if the data object is
     unable to deliver its content more than once (e.g. a file or an
     iterable that can produce the content only once) and the request
     is retried for HTTP redirects or authentication.  The *data* is
     sent to the HTTP server right away after the headers.  There is
     no support for a 100-continue expectation in the library.

   Changed in version 3.3: "Request.method" argument is added to the
   Request class.

   Changed in version 3.4: Default "Request.method" may be indicated
   at the class level.

   Changed in version 3.6: Do not raise an error if the "Content-
   Length" has not been provided and *data* is neither "None" nor a
   bytes object. Fall back to use chunked transfer encoding instead.

class urllib.request.OpenerDirector

   The "OpenerDirector" class opens URLs via "BaseHandler"s chained
   together. It manages the chaining of handlers, and recovery from
   errors.

class urllib.request.BaseHandler

   This is the base class for all registered handlers — and handles
   only the simple mechanics of registration.

class urllib.request.HTTPDefaultErrorHandler

   A class which defines a default handler for HTTP error responses;
   all responses are turned into "HTTPError" exceptions.

class urllib.request.HTTPRedirectHandler

   A class to handle redirections.

class urllib.request.HTTPCookieProcessor(cookiejar=None)

   A class to handle HTTP Cookies.

class urllib.request.ProxyHandler(proxies=None)

   Cause requests to go through a proxy. If *proxies* is given, it
   must be a dictionary mapping protocol names to URLs of proxies. The
   default is to read the list of proxies from the environment
   variables "<protocol>_proxy".  If no proxy environment variables
   are set, then in a Windows environment proxy settings are obtained
   from the registry’s Internet Settings section, and in a Mac OS X
   environment proxy information is retrieved from the OS X System
   Configuration Framework.

   To disable autodetected proxy pass an empty dictionary.

   The "no_proxy" environment variable can be used to specify hosts
   which shouldn’t be reached via proxy; if set, it should be a comma-
   separated list of hostname suffixes, optionally with ":port"
   appended, for example "cern.ch,ncsa.uiuc.edu,some.host:8080".

      Note: "HTTP_PROXY" will be ignored if a variable
        "REQUEST_METHOD" is set; see the documentation on
        "getproxies()".

class urllib.request.HTTPPasswordMgr

   Keep a database of  "(realm, uri) -> (user, password)" mappings.

class urllib.request.HTTPPasswordMgrWithDefaultRealm

   Keep a database of  "(realm, uri) -> (user, password)" mappings. A
   realm of "None" is considered a catch-all realm, which is searched
   if no other realm fits.

class urllib.request.HTTPPasswordMgrWithPriorAuth

   A variant of "HTTPPasswordMgrWithDefaultRealm" that also has a
   database of "uri -> is_authenticated" mappings.  Can be used by a
   BasicAuth handler to determine when to send authentication
   credentials immediately instead of waiting for a "401" response
   first.

   New in version 3.5.

class urllib.request.AbstractBasicAuthHandler(password_mgr=None)

   This is a mixin class that helps with HTTP authentication, both to
   the remote host and to a proxy. *password_mgr*, if given, should be
   something that is compatible with "HTTPPasswordMgr"; refer to
   section HTTPPasswordMgr Objects for information on the interface
   that must be supported.  If *passwd_mgr* also provides
   "is_authenticated" and "update_authenticated" methods (see
   HTTPPasswordMgrWithPriorAuth Objects), then the handler will use
   the "is_authenticated" result for a given URI to determine whether
   or not to send authentication credentials with the request.  If
   "is_authenticated" returns "True" for the URI, credentials are
   sent.  If "is_authenticated" is "False", credentials are not sent,
   and then if a "401" response is received the request is re-sent
   with the authentication credentials.  If authentication succeeds,
   "update_authenticated" is called to set "is_authenticated" "True"
   for the URI, so that subsequent requests to the URI or any of its
   super-URIs will automatically include the authentication
   credentials.

   New in version 3.5: Added "is_authenticated" support.

class urllib.request.HTTPBasicAuthHandler(password_mgr=None)

   Handle authentication with the remote host. *password_mgr*, if
   given, should be something that is compatible with
   "HTTPPasswordMgr"; refer to section HTTPPasswordMgr Objects for
   information on the interface that must be supported.
   HTTPBasicAuthHandler will raise a "ValueError" when presented with
   a wrong Authentication scheme.

class urllib.request.ProxyBasicAuthHandler(password_mgr=None)

   Handle authentication with the proxy. *password_mgr*, if given,
   should be something that is compatible with "HTTPPasswordMgr";
   refer to section HTTPPasswordMgr Objects for information on the
   interface that must be supported.

class urllib.request.AbstractDigestAuthHandler(password_mgr=None)

   This is a mixin class that helps with HTTP authentication, both to
   the remote host and to a proxy. *password_mgr*, if given, should be
   something that is compatible with "HTTPPasswordMgr"; refer to
   section HTTPPasswordMgr Objects for information on the interface
   that must be supported.

class urllib.request.HTTPDigestAuthHandler(password_mgr=None)

   Handle authentication with the remote host. *password_mgr*, if
   given, should be something that is compatible with
   "HTTPPasswordMgr"; refer to section HTTPPasswordMgr Objects for
   information on the interface that must be supported. When both
   Digest Authentication Handler and Basic Authentication Handler are
   both added, Digest Authentication is always tried first. If the
   Digest Authentication returns a 40x response again, it is sent to
   Basic Authentication handler to Handle.  This Handler method will
   raise a "ValueError" when presented with an authentication scheme
   other than Digest or Basic.

   Changed in version 3.3: Raise "ValueError" on unsupported
   Authentication Scheme.

class urllib.request.ProxyDigestAuthHandler(password_mgr=None)

   Handle authentication with the proxy. *password_mgr*, if given,
   should be something that is compatible with "HTTPPasswordMgr";
   refer to section HTTPPasswordMgr Objects for information on the
   interface that must be supported.

class urllib.request.HTTPHandler

   A class to handle opening of HTTP URLs.

class urllib.request.HTTPSHandler(debuglevel=0, context=None, check_hostname=None)

   A class to handle opening of HTTPS URLs.  *context* and
   *check_hostname* have the same meaning as in
   "http.client.HTTPSConnection".

   Changed in version 3.2: *context* and *check_hostname* were added.

class urllib.request.FileHandler

   Open local files.

class urllib.request.DataHandler

   Open data URLs.

   New in version 3.4.

class urllib.request.FTPHandler

   Open FTP URLs.

class urllib.request.CacheFTPHandler

   Open FTP URLs, keeping a cache of open FTP connections to minimize
   delays.

class urllib.request.UnknownHandler

   A catch-all class to handle unknown URLs.

class urllib.request.HTTPErrorProcessor

   Process HTTP error responses.


21.6.1. Request Objects
=======================

The following methods describe "Request"’s public interface, and so
all may be overridden in subclasses.  It also defines several public
attributes that can be used by clients to inspect the parsed request.

Request.full_url

   The original URL passed to the constructor.

   Changed in version 3.4.

   Request.full_url is a property with setter, getter and a deleter.
   Getting "full_url" returns the original request URL with the
   fragment, if it was present.

Request.type

   The URI scheme.

Request.host

   The URI authority, typically a host, but may also contain a port
   separated by a colon.

Request.origin_req_host

   The original host for the request, without port.

Request.selector

   The URI path.  If the "Request" uses a proxy, then selector will be
   the full URL that is passed to the proxy.

Request.data

   The entity body for the request, or "None" if not specified.

   Changed in version 3.4: Changing value of "Request.data" now
   deletes “Content-Length” header if it was previously set or
   calculated.

Request.unverifiable

   boolean, indicates whether the request is unverifiable as defined
   by **RFC 2965**.

Request.method

   The HTTP request method to use.  By default its value is "None",
   which means that "get_method()" will do its normal computation of
   the method to be used.  Its value can be set (thus overriding the
   default computation in "get_method()") either by providing a
   default value by setting it at the class level in a "Request"
   subclass, or by passing a value in to the "Request" constructor via
   the *method* argument.

   New in version 3.3.

   Changed in version 3.4: A default value can now be set in
   subclasses; previously it could only be set via the constructor
   argument.

Request.get_method()

   Return a string indicating the HTTP request method.  If
   "Request.method" is not "None", return its value, otherwise return
   "'GET'" if "Request.data" is "None", or "'POST'" if it’s not. This
   is only meaningful for HTTP requests.

   Changed in version 3.3: get_method now looks at the value of
   "Request.method".

Request.add_header(key, val)

   Add another header to the request.  Headers are currently ignored
   by all handlers except HTTP handlers, where they are added to the
   list of headers sent to the server.  Note that there cannot be more
   than one header with the same name, and later calls will overwrite
   previous calls in case the *key* collides. Currently, this is no
   loss of HTTP functionality, since all headers which have meaning
   when used more than once have a (header-specific) way of gaining
   the same functionality using only one header.

Request.add_unredirected_header(key, header)

   Add a header that will not be added to a redirected request.

Request.has_header(header)

   Return whether the instance has the named header (checks both
   regular and unredirected).

Request.remove_header(header)

   Remove named header from the request instance (both from regular
   and unredirected headers).

   New in version 3.4.

Request.get_full_url()

   Return the URL given in the constructor.

   Changed in version 3.4.

   Returns "Request.full_url"

Request.set_proxy(host, type)

   Prepare the request by connecting to a proxy server. The *host* and
   *type* will replace those of the instance, and the instance’s
   selector will be the original URL given in the constructor.

Request.get_header(header_name, default=None)

   Return the value of the given header. If the header is not present,
   return the default value.

Request.header_items()

   Return a list of tuples (header_name, header_value) of the Request
   headers.

Changed in version 3.4: The request methods add_data, has_data,
get_data, get_type, get_host, get_selector, get_origin_req_host and
is_unverifiable that were deprecated since 3.3 have been removed.


21.6.2. OpenerDirector Objects
==============================

"OpenerDirector" instances have the following methods:

OpenerDirector.add_handler(handler)

   *handler* should be an instance of "BaseHandler".  The following
   methods are searched, and added to the possible chains (note that
   HTTP errors are a special case).

   * "protocol_open()" — signal that the handler knows how to open
     *protocol* URLs.

   * "http_error_type()" — signal that the handler knows how to
     handle HTTP errors with HTTP error code *type*.

   * "protocol_error()" — signal that the handler knows how to
     handle errors from (non-"http") *protocol*.

   * "protocol_request()" — signal that the handler knows how to
     pre- process *protocol* requests.

   * "protocol_response()" — signal that the handler knows how to
     post-process *protocol* responses.

OpenerDirector.open(url, data=None[, timeout])

   Open the given *url* (which can be a request object or a string),
   optionally passing the given *data*. Arguments, return values and
   exceptions raised are the same as those of "urlopen()" (which
   simply calls the "open()" method on the currently installed global
   "OpenerDirector").  The optional *timeout* parameter specifies a
   timeout in seconds for blocking operations like the connection
   attempt (if not specified, the global default timeout setting will
   be used). The timeout feature actually works only for HTTP, HTTPS
   and FTP connections).

OpenerDirector.error(proto, *args)

   Handle an error of the given protocol.  This will call the
   registered error handlers for the given protocol with the given
   arguments (which are protocol specific).  The HTTP protocol is a
   special case which uses the HTTP response code to determine the
   specific error handler; refer to the "http_error_*()" methods of
   the handler classes.

   Return values and exceptions raised are the same as those of
   "urlopen()".

OpenerDirector objects open URLs in three stages:

The order in which these methods are called within each stage is
determined by sorting the handler instances.

1. Every handler with a method named like "protocol_request()" has
   that method called to pre-process the request.

2. Handlers with a method named like "protocol_open()" are called
   to handle the request. This stage ends when a handler either
   returns a non-"None" value (ie. a response), or raises an exception
   (usually "URLError").  Exceptions are allowed to propagate.

   In fact, the above algorithm is first tried for methods named
   "default_open()".  If all such methods return "None", the algorithm
   is repeated for methods named like "protocol_open()".  If all such
   methods return "None", the algorithm is repeated for methods named
   "unknown_open()".

   Note that the implementation of these methods may involve calls of
   the parent "OpenerDirector" instance’s "open()" and "error()"
   methods.

3. Every handler with a method named like "protocol_response()" has
   that method called to post-process the response.


21.6.3. BaseHandler Objects
===========================

"BaseHandler" objects provide a couple of methods that are directly
useful, and others that are meant to be used by derived classes.
These are intended for direct use:

BaseHandler.add_parent(director)

   Add a director as parent.

BaseHandler.close()

   Remove any parents.

The following attribute and methods should only be used by classes
derived from "BaseHandler".

Note: The convention has been adopted that subclasses defining
  "protocol_request()" or "protocol_response()" methods are named
  "*Processor"; all others are named "*Handler".

BaseHandler.parent

   A valid "OpenerDirector", which can be used to open using a
   different protocol, or handle errors.

BaseHandler.default_open(req)

   This method is *not* defined in "BaseHandler", but subclasses
   should define it if they want to catch all URLs.

   This method, if implemented, will be called by the parent
   "OpenerDirector".  It should return a file-like object as described
   in the return value of the "open()" of "OpenerDirector", or "None".
   It should raise "URLError", unless a truly exceptional thing
   happens (for example, "MemoryError" should not be mapped to
   "URLError").

   This method will be called before any protocol-specific open
   method.

BaseHandler.protocol_open(req)

   This method is *not* defined in "BaseHandler", but subclasses
   should define it if they want to handle URLs with the given
   protocol.

   This method, if defined, will be called by the parent
   "OpenerDirector". Return values should be the same as for
   "default_open()".

BaseHandler.unknown_open(req)

   This method is *not* defined in "BaseHandler", but subclasses
   should define it if they want to catch all URLs with no specific
   registered handler to open it.

   This method, if implemented, will be called by the "parent"
   "OpenerDirector".  Return values should be the same as for
   "default_open()".

BaseHandler.http_error_default(req, fp, code, msg, hdrs)

   This method is *not* defined in "BaseHandler", but subclasses
   should override it if they intend to provide a catch-all for
   otherwise unhandled HTTP errors.  It will be called automatically
   by the  "OpenerDirector" getting the error, and should not normally
   be called in other circumstances.

   *req* will be a "Request" object, *fp* will be a file-like object
   with the HTTP error body, *code* will be the three-digit code of
   the error, *msg* will be the user-visible explanation of the code
   and *hdrs* will be a mapping object with the headers of the error.

   Return values and exceptions raised should be the same as those of
   "urlopen()".

BaseHandler.http_error_nnn(req, fp, code, msg, hdrs)

   *nnn* should be a three-digit HTTP error code.  This method is also
   not defined in "BaseHandler", but will be called, if it exists, on
   an instance of a subclass, when an HTTP error with code *nnn*
   occurs.

   Subclasses should override this method to handle specific HTTP
   errors.

   Arguments, return values and exceptions raised should be the same
   as for "http_error_default()".

BaseHandler.protocol_request(req)

   This method is *not* defined in "BaseHandler", but subclasses
   should define it if they want to pre-process requests of the given
   protocol.

   This method, if defined, will be called by the parent
   "OpenerDirector". *req* will be a "Request" object. The return
   value should be a "Request" object.

BaseHandler.protocol_response(req, response)

   This method is *not* defined in "BaseHandler", but subclasses
   should define it if they want to post-process responses of the
   given protocol.

   This method, if defined, will be called by the parent
   "OpenerDirector". *req* will be a "Request" object. *response* will
   be an object implementing the same interface as the return value of
   "urlopen()".  The return value should implement the same interface
   as the return value of "urlopen()".


21.6.4. HTTPRedirectHandler Objects
===================================

Note: Some HTTP redirections require action from this module’s
  client code.  If this is the case, "HTTPError" is raised.  See **RFC
  2616** for details of the precise meanings of the various
  redirection codes.An "HTTPError" exception raised as a security
  consideration if the HTTPRedirectHandler is presented with a
  redirected URL which is not an HTTP, HTTPS or FTP URL.

HTTPRedirectHandler.redirect_request(req, fp, code, msg, hdrs, newurl)

   Return a "Request" or "None" in response to a redirect. This is
   called by the default implementations of the "http_error_30*()"
   methods when a redirection is received from the server.  If a
   redirection should take place, return a new "Request" to allow
   "http_error_30*()" to perform the redirect to *newurl*.  Otherwise,
   raise "HTTPError" if no other handler should try to handle this
   URL, or return "None" if you can’t but another handler might.

   Note: The default implementation of this method does not strictly
     follow **RFC 2616**, which says that 301 and 302 responses to
     "POST" requests must not be automatically redirected without
     confirmation by the user.  In reality, browsers do allow
     automatic redirection of these responses, changing the POST to a
     "GET", and the default implementation reproduces this behavior.

HTTPRedirectHandler.http_error_301(req, fp, code, msg, hdrs)

   Redirect to the "Location:" or "URI:" URL.  This method is called
   by the parent "OpenerDirector" when getting an HTTP ‘moved
   permanently’ response.

HTTPRedirectHandler.http_error_302(req, fp, code, msg, hdrs)

   The same as "http_error_301()", but called for the ‘found’
   response.

HTTPRedirectHandler.http_error_303(req, fp, code, msg, hdrs)

   The same as "http_error_301()", but called for the ‘see other’
   response.

HTTPRedirectHandler.http_error_307(req, fp, code, msg, hdrs)

   The same as "http_error_301()", but called for the ‘temporary
   redirect’ response.


21.6.5. HTTPCookieProcessor Objects
===================================

"HTTPCookieProcessor" instances have one attribute:

HTTPCookieProcessor.cookiejar

   The "http.cookiejar.CookieJar" in which cookies are stored.


21.6.6. ProxyHandler Objects
============================

ProxyHandler.protocol_open(request)

   The "ProxyHandler" will have a method "protocol_open()" for every
   *protocol* which has a proxy in the *proxies* dictionary given in
   the constructor.  The method will modify requests to go through the
   proxy, by calling "request.set_proxy()", and call the next handler
   in the chain to actually execute the protocol.


21.6.7. HTTPPasswordMgr Objects
===============================

These methods are available on "HTTPPasswordMgr" and
"HTTPPasswordMgrWithDefaultRealm" objects.

HTTPPasswordMgr.add_password(realm, uri, user, passwd)

   *uri* can be either a single URI, or a sequence of URIs. *realm*,
   *user* and *passwd* must be strings. This causes "(user, passwd)"
   to be used as authentication tokens when authentication for *realm*
   and a super-URI of any of the given URIs is given.

HTTPPasswordMgr.find_user_password(realm, authuri)

   Get user/password for given realm and URI, if any.  This method
   will return "(None, None)" if there is no matching user/password.

   For "HTTPPasswordMgrWithDefaultRealm" objects, the realm "None"
   will be searched if the given *realm* has no matching
   user/password.


21.6.8. HTTPPasswordMgrWithPriorAuth Objects
============================================

This password manager extends "HTTPPasswordMgrWithDefaultRealm" to
support tracking URIs for which authentication credentials should
always be sent.

HTTPPasswordMgrWithPriorAuth.add_password(realm, uri, user, passwd, is_authenticated=False)

   *realm*, *uri*, *user*, *passwd* are as for
   "HTTPPasswordMgr.add_password()".  *is_authenticated* sets the
   initial value of the "is_authenticated" flag for the given URI or
   list of URIs. If *is_authenticated* is specified as "True", *realm*
   is ignored.

HTTPPasswordMgr.find_user_password(realm, authuri)

   Same as for "HTTPPasswordMgrWithDefaultRealm" objects

HTTPPasswordMgrWithPriorAuth.update_authenticated(self, uri, is_authenticated=False)

   Update the "is_authenticated" flag for the given *uri* or list of
   URIs.

HTTPPasswordMgrWithPriorAuth.is_authenticated(self, authuri)

   Returns the current state of the "is_authenticated" flag for the
   given URI.


21.6.9. AbstractBasicAuthHandler Objects
========================================

AbstractBasicAuthHandler.http_error_auth_reqed(authreq, host, req, headers)

   Handle an authentication request by getting a user/password pair,
   and re-trying the request.  *authreq* should be the name of the
   header where the information about the realm is included in the
   request, *host* specifies the URL and path to authenticate for,
   *req* should be the (failed) "Request" object, and *headers* should
   be the error headers.

   *host* is either an authority (e.g. ""python.org"") or a URL
   containing an authority component (e.g. ""http://python.org/""). In
   either case, the authority must not contain a userinfo component
   (so, ""python.org"" and ""python.org:80"" are fine,
   ""joe:password@python.org"" is not).


21.6.10. HTTPBasicAuthHandler Objects
=====================================

HTTPBasicAuthHandler.http_error_401(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


21.6.11. ProxyBasicAuthHandler Objects
======================================

ProxyBasicAuthHandler.http_error_407(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


21.6.12. AbstractDigestAuthHandler Objects
==========================================

AbstractDigestAuthHandler.http_error_auth_reqed(authreq, host, req, headers)

   *authreq* should be the name of the header where the information
   about the realm is included in the request, *host* should be the
   host to authenticate to, *req* should be the (failed) "Request"
   object, and *headers* should be the error headers.


21.6.13. HTTPDigestAuthHandler Objects
======================================

HTTPDigestAuthHandler.http_error_401(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


21.6.14. ProxyDigestAuthHandler Objects
=======================================

ProxyDigestAuthHandler.http_error_407(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


21.6.15. HTTPHandler Objects
============================

HTTPHandler.http_open(req)

   Send an HTTP request, which can be either GET or POST, depending on
   "req.has_data()".


21.6.16. HTTPSHandler Objects
=============================

HTTPSHandler.https_open(req)

   Send an HTTPS request, which can be either GET or POST, depending
   on "req.has_data()".


21.6.17. FileHandler Objects
============================

FileHandler.file_open(req)

   Open the file locally, if there is no host name, or the host name
   is "'localhost'".

   Changed in version 3.2: This method is applicable only for local
   hostnames.  When a remote hostname is given, an "URLError" is
   raised.


21.6.18. DataHandler Objects
============================

DataHandler.data_open(req)

   Read a data URL. This kind of URL contains the content encoded in
   the URL itself. The data URL syntax is specified in **RFC 2397**.
   This implementation ignores white spaces in base64 encoded data
   URLs so the URL may be wrapped in whatever source file it comes
   from. But even though some browsers don’t mind about a missing
   padding at the end of a base64 encoded data URL, this
   implementation will raise an "ValueError" in that case.


21.6.19. FTPHandler Objects
===========================

FTPHandler.ftp_open(req)

   Open the FTP file indicated by *req*. The login is always done with
   empty username and password.


21.6.20. CacheFTPHandler Objects
================================

"CacheFTPHandler" objects are "FTPHandler" objects with the following
additional methods:

CacheFTPHandler.setTimeout(t)

   Set timeout of connections to *t* seconds.

CacheFTPHandler.setMaxConns(m)

   Set maximum number of cached connections to *m*.


21.6.21. UnknownHandler Objects
===============================

UnknownHandler.unknown_open()

   Raise a "URLError" exception.


21.6.22. HTTPErrorProcessor Objects
===================================

HTTPErrorProcessor.http_response(request, response)

   Process HTTP error responses.

   For 200 error codes, the response object is returned immediately.

   For non-200 error codes, this simply passes the job on to the
   "protocol_error_code()" handler methods, via
   "OpenerDirector.error()". Eventually, "HTTPDefaultErrorHandler"
   will raise an "HTTPError" if no other handler handles the error.

HTTPErrorProcessor.https_response(request, response)

   Process HTTPS error responses.

   The behavior is same as "http_response()".


21.6.23. Examples
=================

In addition to the examples below, more examples are given in HOWTO
Fetch Internet Resources Using The urllib Package.

This example gets the python.org main page and displays the first 300
bytes of it.

   >>> import urllib.request
   >>> with urllib.request.urlopen('http://www.python.org/') as f:
   ...     print(f.read(300))
   ...
   b'<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">\n\n\n<html
   xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">\n\n<head>\n
   <meta http-equiv="content-type" content="text/html; charset=utf-8" />\n
   <title>Python Programming '

Note that urlopen returns a bytes object.  This is because there is no
way for urlopen to automatically determine the encoding of the byte
stream it receives from the HTTP server. In general, a program will
decode the returned bytes object to string once it determines or
guesses the appropriate encoding.

The following W3C document,
https://www.w3.org/International/O-charset, lists the various ways in
which an (X)HTML or an XML document could have specified its encoding
information.

As the python.org website uses *utf-8* encoding as specified in its
meta tag, we will use the same for decoding the bytes object.

   >>> with urllib.request.urlopen('http://www.python.org/') as f:
   ...     print(f.read(100).decode('utf-8'))
   ...
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtm

It is also possible to achieve the same result without using the
*context manager* approach.

   >>> import urllib.request
   >>> f = urllib.request.urlopen('http://www.python.org/')
   >>> print(f.read(100).decode('utf-8'))
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtm

In the following example, we are sending a data-stream to the stdin of
a CGI and reading the data it returns to us. Note that this example
will only work when the Python installation supports SSL.

   >>> import urllib.request
   >>> req = urllib.request.Request(url='https://localhost/cgi-bin/test.cgi',
   ...                       data=b'This data is passed to stdin of the CGI')
   >>> with urllib.request.urlopen(req) as f:
   ...     print(f.read().decode('utf-8'))
   ...
   Got Data: "This data is passed to stdin of the CGI"

The code for the sample CGI used in the above example is:

   #!/usr/bin/env python
   import sys
   data = sys.stdin.read()
   print('Content-type: text/plain\n\nGot Data: "%s"' % data)

Here is an example of doing a "PUT" request using "Request":

   import urllib.request
   DATA = b'some data'
   req = urllib.request.Request(url='http://localhost:8080', data=DATA,method='PUT')
   with urllib.request.urlopen(req) as f:
       pass
   print(f.status)
   print(f.reason)

Use of Basic HTTP Authentication:

   import urllib.request
   # Create an OpenerDirector with support for Basic HTTP Authentication...
   auth_handler = urllib.request.HTTPBasicAuthHandler()
   auth_handler.add_password(realm='PDQ Application',
                             uri='https://mahler:8092/site-updates.py',
                             user='klem',
                             passwd='kadidd!ehopper')
   opener = urllib.request.build_opener(auth_handler)
   # ...and install it globally so it can be used with urlopen.
   urllib.request.install_opener(opener)
   urllib.request.urlopen('http://www.example.com/login.html')

"build_opener()" provides many handlers by default, including a
"ProxyHandler".  By default, "ProxyHandler" uses the environment
variables named "<scheme>_proxy", where "<scheme>" is the URL scheme
involved.  For example, the "http_proxy" environment variable is read
to obtain the HTTP proxy’s URL.

This example replaces the default "ProxyHandler" with one that uses
programmatically-supplied proxy URLs, and adds proxy authorization
support with "ProxyBasicAuthHandler".

   proxy_handler = urllib.request.ProxyHandler({'http': 'http://www.example.com:3128/'})
   proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
   proxy_auth_handler.add_password('realm', 'host', 'username', 'password')

   opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
   # This time, rather than install the OpenerDirector, we use it directly:
   opener.open('http://www.example.com/login.html')

Adding HTTP headers:

Use the *headers* argument to the "Request" constructor, or:

   import urllib.request
   req = urllib.request.Request('http://www.example.com/')
   req.add_header('Referer', 'http://www.python.org/')
   # Customize the default User-Agent header value:
   req.add_header('User-Agent', 'urllib-example/0.1 (Contact: . . .)')
   r = urllib.request.urlopen(req)

"OpenerDirector" automatically adds a *User-Agent* header to every
"Request".  To change this:

   import urllib.request
   opener = urllib.request.build_opener()
   opener.addheaders = [('User-agent', 'Mozilla/5.0')]
   opener.open('http://www.example.com/')

Also, remember that a few standard headers (*Content-Length*,
*Content-Type* and *Host*) are added when the "Request" is passed to
"urlopen()" (or "OpenerDirector.open()").

Here is an example session that uses the "GET" method to retrieve a
URL containing parameters:

   >>> import urllib.request
   >>> import urllib.parse
   >>> params = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
   >>> url = "http://www.musi-cal.com/cgi-bin/query?%s" % params
   >>> with urllib.request.urlopen(url) as f:
   ...     print(f.read().decode('utf-8'))
   ...

The following example uses the "POST" method instead. Note that params
output from urlencode is encoded to bytes before it is sent to urlopen
as data:

   >>> import urllib.request
   >>> import urllib.parse
   >>> data = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
   >>> data = data.encode('ascii')
   >>> with urllib.request.urlopen("http://requestb.in/xrbl82xr", data) as f:
   ...     print(f.read().decode('utf-8'))
   ...

The following example uses an explicitly specified HTTP proxy,
overriding environment settings:

   >>> import urllib.request
   >>> proxies = {'http': 'http://proxy.example.com:8080/'}
   >>> opener = urllib.request.FancyURLopener(proxies)
   >>> with opener.open("http://www.python.org") as f:
   ...     f.read().decode('utf-8')
   ...

The following example uses no proxies at all, overriding environment
settings:

   >>> import urllib.request
   >>> opener = urllib.request.FancyURLopener({})
   >>> with opener.open("http://www.python.org/") as f:
   ...     f.read().decode('utf-8')
   ...


21.6.24. Legacy interface
=========================

The following functions and classes are ported from the Python 2
module "urllib" (as opposed to "urllib2").  They might become
deprecated at some point in the future.

urllib.request.urlretrieve(url, filename=None, reporthook=None, data=None)

   Copy a network object denoted by a URL to a local file. If the URL
   points to a local file, the object will not be copied unless
   filename is supplied. Return a tuple "(filename, headers)" where
   *filename* is the local file name under which the object can be
   found, and *headers* is whatever the "info()" method of the object
   returned by "urlopen()" returned (for a remote object). Exceptions
   are the same as for "urlopen()".

   The second argument, if present, specifies the file location to
   copy to (if absent, the location will be a tempfile with a
   generated name). The third argument, if present, is a callable that
   will be called once on establishment of the network connection and
   once after each block read thereafter.  The callable will be passed
   three arguments; a count of blocks transferred so far, a block size
   in bytes, and the total size of the file.  The third argument may
   be "-1" on older FTP servers which do not return a file size in
   response to a retrieval request.

   The following example illustrates the most common usage scenario:

      >>> import urllib.request
      >>> local_filename, headers = urllib.request.urlretrieve('http://python.org/')
      >>> html = open(local_filename)
      >>> html.close()

   If the *url* uses the "http:" scheme identifier, the optional
   *data* argument may be given to specify a "POST" request (normally
   the request type is "GET").  The *data* argument must be a bytes
   object in standard *application/x-www-form-urlencoded* format; see
   the "urllib.parse.urlencode()" function.

   "urlretrieve()" will raise "ContentTooShortError" when it detects
   that the amount of data available  was less than the expected
   amount (which is the size reported by a  *Content-Length* header).
   This can occur, for example, when the  download is interrupted.

   The *Content-Length* is treated as a lower bound: if there’s more
   data  to read, urlretrieve reads more data, but if less data is
   available,  it raises the exception.

   You can still retrieve the downloaded data in this case, it is
   stored  in the "content" attribute of the exception instance.

   If no *Content-Length* header was supplied, urlretrieve can not
   check the size of the data it has downloaded, and just returns it.
   In this case you just have to assume that the download was
   successful.

urllib.request.urlcleanup()

   Cleans up temporary files that may have been left behind by
   previous calls to "urlretrieve()".

class urllib.request.URLopener(proxies=None, **x509)

   Deprecated since version 3.3.

   Base class for opening and reading URLs.  Unless you need to
   support opening objects using schemes other than "http:", "ftp:",
   or "file:", you probably want to use "FancyURLopener".

   By default, the "URLopener" class sends a *User-Agent* header of
   "urllib/VVV", where *VVV* is the "urllib" version number.
   Applications can define their own *User-Agent* header by
   subclassing "URLopener" or "FancyURLopener" and setting the class
   attribute "version" to an appropriate string value in the subclass
   definition.

   The optional *proxies* parameter should be a dictionary mapping
   scheme names to proxy URLs, where an empty dictionary turns proxies
   off completely.  Its default value is "None", in which case
   environmental proxy settings will be used if present, as discussed
   in the definition of "urlopen()", above.

   Additional keyword parameters, collected in *x509*, may be used for
   authentication of the client when using the "https:" scheme.  The
   keywords *key_file* and *cert_file* are supported to provide an
   SSL key and certificate; both are needed to support client
   authentication.

   "URLopener" objects will raise an "OSError" exception if the server
   returns an error code.

   open(fullurl, data=None)

      Open *fullurl* using the appropriate protocol.  This method sets
      up cache and proxy information, then calls the appropriate open
      method with its input arguments.  If the scheme is not
      recognized, "open_unknown()" is called. The *data* argument has
      the same meaning as the *data* argument of "urlopen()".

   open_unknown(fullurl, data=None)

      Overridable interface to open unknown URL types.

   retrieve(url, filename=None, reporthook=None, data=None)

      Retrieves the contents of *url* and places it in *filename*.
      The return value is a tuple consisting of a local filename and
      either an "email.message.Message" object containing the response
      headers (for remote URLs) or "None" (for local URLs).  The
      caller must then open and read the contents of *filename*.  If
      *filename* is not given and the URL refers to a local file, the
      input filename is returned.  If the URL is non-local and
      *filename* is not given, the filename is the output of
      "tempfile.mktemp()" with a suffix that matches the suffix of the
      last path component of the input URL.  If *reporthook* is given,
      it must be a function accepting three numeric parameters: A
      chunk number, the maximum size chunks are read in and the total
      size of the download (-1 if unknown).  It will be called once at
      the start and after each chunk of data is read from the network.
      *reporthook* is ignored for local URLs.

      If the *url* uses the "http:" scheme identifier, the optional
      *data* argument may be given to specify a "POST" request
      (normally the request type is "GET").  The *data* argument must
      in standard *application/x-www-form-urlencoded* format; see the
      "urllib.parse.urlencode()" function.

   version

      Variable that specifies the user agent of the opener object.  To
      get "urllib" to tell servers that it is a particular user agent,
      set this in a subclass as a class variable or in the constructor
      before calling the base constructor.

class urllib.request.FancyURLopener(...)

   Deprecated since version 3.3.

   "FancyURLopener" subclasses "URLopener" providing default handling
   for the following HTTP response codes: 301, 302, 303, 307 and 401.
   For the 30x response codes listed above, the *Location* header is
   used to fetch the actual URL.  For 401 response codes
   (authentication required), basic HTTP authentication is performed.
   For the 30x response codes, recursion is bounded by the value of
   the *maxtries* attribute, which defaults to 10.

   For all other response codes, the method "http_error_default()" is
   called which you can override in subclasses to handle the error
   appropriately.

   Note: According to the letter of **RFC 2616**, 301 and 302
     responses to POST requests must not be automatically redirected
     without confirmation by the user.  In reality, browsers do allow
     automatic redirection of these responses, changing the POST to a
     GET, and "urllib" reproduces this behaviour.

   The parameters to the constructor are the same as those for
   "URLopener".

   Note: When performing basic authentication, a "FancyURLopener"
     instance calls its "prompt_user_passwd()" method.  The default
     implementation asks the users for the required information on the
     controlling terminal.  A subclass may override this method to
     support more appropriate behavior if needed.

   The "FancyURLopener" class offers one additional method that should
   be overloaded to provide the appropriate behavior:

   prompt_user_passwd(host, realm)

      Return information needed to authenticate the user at the given
      host in the specified security realm.  The return value should
      be a tuple, "(user, password)", which can be used for basic
      authentication.

      The implementation prompts for this information on the terminal;
      an application should override this method to use an appropriate
      interaction model in the local environment.


21.6.25. "urllib.request" Restrictions
======================================

* Currently, only the following protocols are supported: HTTP
  (versions 0.9 and 1.0), FTP, local files, and data URLs.

  Changed in version 3.4: Added support for data URLs.

* The caching feature of "urlretrieve()" has been disabled until
  someone finds the time to hack proper processing of Expiration time
  headers.

* There should be a function to query whether a particular URL is in
  the cache.

* For backward compatibility, if a URL appears to point to a local
  file but the file can’t be opened, the URL is re-interpreted using
  the FTP protocol.  This can sometimes cause confusing error
  messages.

* The "urlopen()" and "urlretrieve()" functions can cause
  arbitrarily long delays while waiting for a network connection to be
  set up. This means that it is difficult to build an interactive Web
  client using these functions without using threads.

* The data returned by "urlopen()" or "urlretrieve()" is the raw
  data returned by the server.  This may be binary data (such as an
  image), plain text or (for example) HTML.  The HTTP protocol
  provides type information in the reply header, which can be
  inspected by looking at the *Content-Type* header.  If the returned
  data is HTML, you can use the module "html.parser" to parse it.

* The code handling the FTP protocol cannot differentiate between a
  file and a directory.  This can lead to unexpected behavior when
  attempting to read a URL that points to a file that is not
  accessible.  If the URL ends in a "/", it is assumed to refer to a
  directory and will be handled accordingly.  But if an attempt to
  read a file leads to a 550 error (meaning the URL cannot be found or
  is not accessible, often for permission reasons), then the path is
  treated as a directory in order to handle the case when a directory
  is specified by a URL but the trailing "/" has been left off.  This
  can cause misleading results when you try to fetch a file whose read
  permissions make it inaccessible; the FTP code will try to read it,
  fail with a 550 error, and then perform a directory listing for the
  unreadable file. If fine-grained control is needed, consider using
  the "ftplib" module, subclassing "FancyURLopener", or changing
  *_urlopener* to meet your needs.


21.7. "urllib.response" — Response classes used by urllib
*********************************************************

The "urllib.response" module defines functions and classes which
define a minimal file like interface, including "read()" and
"readline()". The typical response object is an addinfourl instance,
which defines an "info()" method and that returns headers and a
"geturl()" method that returns the url. Functions defined by this
module are used internally by the "urllib.request" module.
