# 21.16. `nntplib` — NNTP protocol client

Source code: Lib/nntplib.py

This module defines the class `NNTP` which implements the client side of the Network News Transfer Protocol. It can be used to implement a news reader or poster, or automated news processors. It is compatible with RFC 3977 as well as the older RFC 977 and RFC 2980.

Here are two small examples of how it can be used. To list some statistics about a newsgroup and print the subjects of the last 10 articles:

    >>> s = nntplib.NNTP('news.gmane.org')
    >>> resp, count, first, last, name = s.group('gmane.comp.python.committers')
    >>> print('Group', name, 'has', count, 'articles, range', first, 'to', last)
    Group gmane.comp.python.committers has 1096 articles, range 1 to 1096
    >>> resp, overviews = s.over((last - 9, last))
    >>> for id, over in overviews:
    ...     print(id, nntplib.decode_header(over['subject']))
    ...
    1087 Re: Commit privileges for Łukasz Langa
    1088 Re: 3.2 alpha 2 freeze
    1089 Re: 3.2 alpha 2 freeze
    1090 Re: Commit privileges for Łukasz Langa
    1091 Re: Commit privileges for Łukasz Langa
    1092 Updated ssh key
    1093 Re: Updated ssh key
    1094 Re: Updated ssh key
    1095 Hello fellow committers!
    1096 Re: Hello fellow committers!
    >>> s.quit()
    '205 Bye!'

To post an article from a binary file (this assumes that the article has valid headers, and that you have right to post on the particular newsgroup):

    >>> s = nntplib.NNTP('news.gmane.org')
    >>> f = open('article.txt', 'rb')
    >>> s.post(f)
    '240 Article posted successfully.'
    >>> s.quit()
    '205 Bye!'

The module itself defines the following classes:

class `nntplib.``NNTP`(host, port=119, user=None, password=None, readermode=None, usenetrc=False[, timeout])

  Return a new `NNTP` object, representing a connection to the NNTP server running on host host, listening at port port. An optional timeout can be specified for the socket connection. If the optional user and password are provided, or if suitable credentials are present in `/.netrc` and the optional flag usenetrc is true, the `AUTHINFO USER` and `AUTHINFO PASS` commands are used to identify and authenticate the user to the server. If the optional flag readermode is true, then a `mode reader` command is sent before authentication is performed. Reader mode is sometimes necessary if you are connecting to an NNTP server on the local machine and intend to call reader-specific commands, such as `group`. If you get unexpected `NNTPPermanentError`s, you might need to set readermode. The `NNTP` class supports the `with` statement to unconditionally consume `OSError` exceptions and to close the NNTP connection when done, e.g.:

      >>> from nntplib import NNTP
      >>> with NNTP('news.gmane.org') as n:
      ...     n.group('gmane.comp.python.committers')
      ...
      ('211 1755 1 1755 gmane.comp.python.committers', 1755, 1, 1755, 'gmane.comp.python.committers')
      >>>

  Changed in version 3.2: usenetrc is now `False` by default.

  Changed in version 3.3: Support for the `with` statement was added.

class `nntplib.``NNTP_SSL`(host, port=563, user=None, password=None, ssl_context=None, readermode=None, usenetrc=False[, timeout])

  Return a new `NNTP_SSL` object, representing an encrypted connection to the NNTP server running on host host, listening at port port. `NNTP_SSL` objects have the same methods as `NNTP` objects. If port is omitted, port 563 (NNTPS) is used. ssl_context is also optional, and is a `SSLContext` object. Please read Security considerations for best practices. All other parameters behave the same as for `NNTP`.

  Note that SSL-on-563 is discouraged per RFC 4642, in favor of STARTTLS as described below. However, some servers only support the former.

  New in version 3.2.

  Changed in version 3.4: The class now supports hostname check with `ssl.SSLContext.check_hostname` and Server Name Indication (see `ssl.HAS_SNI`).

exception `nntplib.``NNTPError`

  Derived from the standard exception `Exception`, this is the base class for all exceptions raised by the `nntplib` module. Instances of this class have the following attribute:

  `response`

    The response of the server if available, as a `str` object.

exception `nntplib.``NNTPReplyError`

  Exception raised when an unexpected reply is received from the server.

exception `nntplib.``NNTPTemporaryError`

  Exception raised when a response code in the range 400–499 is received.

exception `nntplib.``NNTPPermanentError`

  Exception raised when a response code in the range 500–599 is received.

exception `nntplib.``NNTPProtocolError`

  Exception raised when a reply is received from the server that does not begin with a digit in the range 1–5.

exception `nntplib.``NNTPDataError`

  Exception raised when there is some error in the response data.

## 21.16.1. NNTP Objects

When connected, `NNTP` and `NNTP_SSL` objects support the following methods and attributes.

### 21.16.1.1. Attributes

`NNTP.``nntp_version`

  An integer representing the version of the NNTP protocol supported by the server. In practice, this should be `2` for servers advertising RFC 3977 compliance and `1` for others.

  New in version 3.2.

`NNTP.``nntp_implementation`

  A string describing the software name and version of the NNTP server, or `None` if not advertised by the server.

  New in version 3.2.

### 21.16.1.2. Methods

The response that is returned as the first item in the return tuple of almost all methods is the server’s response: a string beginning with a three-digit code. If the server’s response indicates an error, the method raises one of the above exceptions.

Many of the following methods take an optional keyword-only argument file. When the file argument is supplied, it must be either a file object opened for binary writing, or the name of an on-disk file to be written to. The method will then write any data returned by the server (except for the response line and the terminating dot) to the file; any list of lines, tuples or objects that the method normally returns will be empty.

Changed in version 3.2: Many of the following methods have been reworked and fixed, which makes them incompatible with their 3.1 counterparts.

`NNTP.``quit`()

  Send a `QUIT` command and close the connection. Once this method has been called, no other methods of the NNTP object should be called.

`NNTP.``getwelcome`()

  Return the welcome message sent by the server in reply to the initial connection. (This message sometimes contains disclaimers or help information that may be relevant to the user.)

`NNTP.``getcapabilities`()

  Return the RFC 3977 capabilities advertised by the server, as a `dict` instance mapping capability names to (possibly empty) lists of values. On legacy servers which don’t understand the `CAPABILITIES` command, an empty dictionary is returned instead.

      >>> s = NNTP('news.gmane.org')
      >>> 'POST' in s.getcapabilities()
      True

  New in version 3.2.

`NNTP.``login`(user=None, password=None, usenetrc=True)

  Send `AUTHINFO` commands with the user name and password. If user and password are `None` and usenetrc is true, credentials from `~/.netrc` will be used if possible.

  Unless intentionally delayed, login is normally performed during the `NNTP` object initialization and separately calling this function is unnecessary. To force authentication to be delayed, you must not set user or password when creating the object, and must set usenetrc to False.

  New in version 3.2.

`NNTP.``starttls`(context=None)

  Send a `STARTTLS` command. This will enable encryption on the NNTP connection. The context argument is optional and should be a `ssl.SSLContext` object. Please read Security considerations for best practices.

  Note that this may not be done after authentication information has been transmitted, and authentication occurs by default if possible during a `NNTP` object initialization. See `NNTP.login()` for information on suppressing this behavior.

  New in version 3.2.

  Changed in version 3.4: The method now supports hostname check with `ssl.SSLContext.check_hostname` and Server Name Indication (see `ssl.HAS_SNI`).

`NNTP.``newgroups`(date, *, file=None)

  Send a `NEWGROUPS` command. The date argument should be a `datetime.date` or `datetime.datetime` object. Return a pair `(response, groups)` where groups is a list representing the groups that are new since the given date. If file is supplied, though, then groups will be empty.

      >>> from datetime import date, timedelta
      >>> resp, groups = s.newgroups(date.today() - timedelta(days=3))
      >>> len(groups)
      85
      >>> groups[0]
      GroupInfo(group='gmane.network.tor.devel', last='4', first='1', flag='m')

`NNTP.``newnews`(group, date, *, file=None)

  Send a `NEWNEWS` command. Here, group is a group name or `'*'`, and date has the same meaning as for `newgroups()`. Return a pair `(response, articles)` where articles is a list of message ids.

  This command is frequently disabled by NNTP server administrators.

`NNTP.``list`(group_pattern=None, *, file=None)

  Send a `LIST` or `LIST ACTIVE` command. Return a pair `(response, list)` where list is a list of tuples representing all the groups available from this NNTP server, optionally matching the pattern string group_pattern. Each tuple has the form `(group, last, first, flag)`, where group is a group name, last and first are the last and first article numbers, and flag usually takes one of these values:

  - `y`: Local postings and articles from peers are allowed.

  - `m`: The group is moderated and all postings must be approved.

  - `n`: No local postings are allowed, only articles from peers.

  - `j`: Articles from peers are filed in the junk group instead.

  - `x`: No local postings, and articles from peers are ignored.

  - `=foo.bar`: Articles are filed in the `foo.bar` group instead.

  If flag has another value, then the status of the newsgroup should be considered unknown.

  This command can return very large results, especially if group_pattern is not specified. It is best to cache the results offline unless you really need to refresh them.

  Changed in version 3.2: group_pattern was added.

`NNTP.``descriptions`(grouppattern)

  Send a `LIST NEWSGROUPS` command, where grouppattern is a wildmat string as specified in RFC 3977 (it’s essentially the same as DOS or UNIX shell wildcard strings). Return a pair `(response, descriptions)`, where descriptions is a dictionary mapping group names to textual descriptions.

      >>> resp, descs = s.descriptions('gmane.comp.python.*')
      >>> len(descs)
      295
      >>> descs.popitem()
      ('gmane.comp.python.bio.general', 'BioPython discussion list (Moderated)')

`NNTP.``description`(group)

  Get a description for a single group group. If more than one group matches (if ‘group’ is a real wildmat string), return the first match. If no group matches, return an empty string.

  This elides the response code from the server. If the response code is needed, use `descriptions()`.

`NNTP.``group`(name)

  Send a `GROUP` command, where name is the group name. The group is selected as the current group, if it exists. Return a tuple `(response, count, first, last, name)` where count is the (estimated) number of articles in the group, first is the first article number in the group, last is the last article number in the group, and name is the group name.

`NNTP.``over`(message_spec, *, file=None)

  Send an `OVER` command, or an `XOVER` command on legacy servers. message_spec can be either a string representing a message id, or a `(first, last)` tuple of numbers indicating a range of articles in the current group, or a `(first, None)` tuple indicating a range of articles starting from first to the last article in the current group, or `None` to select the current article in the current group.

  Return a pair `(response, overviews)`. overviews is a list of `(article_number, overview)` tuples, one for each article selected by message_spec. Each overview is a dictionary with the same number of items, but this number depends on the server. These items are either message headers (the key is then the lower-cased header name) or metadata items (the key is then the metadata name prepended with `":"`). The following items are guaranteed to be present by the NNTP specification:

  - the `subject`, `from`, `date`, `message-id` and `references` headers

  - the `:bytes` metadata: the number of bytes in the entire raw article (including headers and body)

  - the `:lines` metadata: the number of lines in the article body

  The value of each item is either a string, or `None` if not present.

  It is advisable to use the `decode_header()` function on header values when they may contain non-ASCII characters:

      >>> _, _, first, last, _ = s.group('gmane.comp.python.devel')
      >>> resp, overviews = s.over((last, last))
      >>> art_num, over = overviews[0]
      >>> art_num
      117216
      >>> list(over.keys())
      ['xref', 'from', ':lines', ':bytes', 'references', 'date', 'message-id', 'subject']
      >>> over['from']
      '=?UTF-8?B?Ik1hcnRpbiB2LiBMw7Z3aXMi?= <martin@v.loewis.de>'
      >>> nntplib.decode_header(over['from'])
      '"Martin v. Löwis" <martin@v.loewis.de>'

  New in version 3.2.

`NNTP.``help`(*, file=None)

  Send a `HELP` command. Return a pair `(response, list)` where list is a list of help strings.

`NNTP.``stat`(message_spec=None)

  Send a `STAT` command, where message_spec is either a message id (enclosed in `'<'` and `'>'`) or an article number in the current group. If message_spec is omitted or `None`, the current article in the current group is considered. Return a triple `(response, number, id)` where number is the article number and id is the message id.

      >>> _, _, first, last, _ = s.group('gmane.comp.python.devel')
      >>> resp, number, message_id = s.stat(first)
      >>> number, message_id
      (9099, '<20030112190404.GE29873@epoch.metaslash.com>')

`NNTP.``next`()

  Send a `NEXT` command. Return as for `stat()`.

`NNTP.``last`()

  Send a `LAST` command. Return as for `stat()`.

`NNTP.``article`(message_spec=None, *, file=None)

  Send an `ARTICLE` command, where message_spec has the same meaning as for `stat()`. Return a tuple `(response, info)` where info is a `namedtuple` with three attributes number, message_id and lines (in that order). number is the article number in the group (or 0 if the information is not available), message_id the message id as a string, and lines a list of lines (without terminating newlines) comprising the raw message including headers and body.

      >>> resp, info = s.article('<20030112190404.GE29873@epoch.metaslash.com>')
      >>> info.number
      0
      >>> info.message_id
      '<20030112190404.GE29873@epoch.metaslash.com>'
      >>> len(info.lines)
      65
      >>> info.lines[0]
      b'Path: main.gmane.org!not-for-mail'
      >>> info.lines[1]
      b'From: Neal Norwitz <neal@metaslash.com>'
      >>> info.lines[-3:]
      [b'There is a patch for 2.3 as well as 2.2.', b'', b'Neal']

`NNTP.``head`(message_spec=None, *, file=None)

  Same as `article()`, but sends a `HEAD` command. The lines returned (or written to file) will only contain the message headers, not the body.

`NNTP.``body`(message_spec=None, *, file=None)

  Same as `article()`, but sends a `BODY` command. The lines returned (or written to file) will only contain the message body, not the headers.

`NNTP.``post`(data)

  Post an article using the `POST` command. The data argument is either a file object opened for binary reading, or any iterable of bytes objects (representing raw lines of the article to be posted). It should represent a well-formed news article, including the required headers. The `post()` method automatically escapes lines beginning with `.` and appends the termination line.

  If the method succeeds, the server’s response is returned. If the server refuses posting, a `NNTPReplyError` is raised.

`NNTP.``ihave`(message_id, data)

  Send an `IHAVE` command. message_id is the id of the message to send to the server (enclosed in `'<'` and `'>'`). The data parameter and the return value are the same as for `post()`.

`NNTP.``date`()

  Return a pair `(response, date)`. date is a `datetime` object containing the current date and time of the server.

`NNTP.``slave`()

  Send a `SLAVE` command. Return the server’s response.

`NNTP.``set_debuglevel`(level)

  Set the instance’s debugging level. This controls the amount of debugging output printed. The default, `0`, produces no debugging output. A value of `1` produces a moderate amount of debugging output, generally a single line per request or response. A value of `2` or higher produces the maximum amount of debugging output, logging each line sent and received on the connection (including message text).

The following are optional NNTP extensions defined in RFC 2980. Some of them have been superseded by newer commands in RFC 3977.

`NNTP.``xhdr`(hdr, str, *, file=None)

  Send an `XHDR` command. The hdr argument is a header keyword, e.g. `'subject'`. The str argument should have the form `'first-last'` where first and last are the first and last article numbers to search. Return a pair `(response, list)`, where list is a list of pairs `(id, text)`, where id is an article number (as a string) and text is the text of the requested header for that article. If the file parameter is supplied, then the output of the `XHDR` command is stored in a file. If file is a string, then the method will open a file with that name, write to it then close it. If file is a file object, then it will start calling `write()` on it to store the lines of the command output. If file is supplied, then the returned list is an empty list.

`NNTP.``xover`(start, end, *, file=None)

  Send an `XOVER` command. start and end are article numbers delimiting the range of articles to select. The return value is the same of for `over()`. It is recommended to use `over()` instead, since it will automatically use the newer `OVER` command if available.

`NNTP.``xpath`(id)

  Return a pair `(resp, path)`, where path is the directory path to the article with message ID id. Most of the time, this extension is not enabled by NNTP server administrators.

  Deprecated since version 3.3: The XPATH extension is not actively used.

## 21.16.2. Utility functions

The module also defines the following utility function:

`nntplib.``decode_header`(header_str)

  Decode a header value, un-escaping any escaped non-ASCII characters. header_str must be a `str` object. The unescaped value is returned. Using this function is recommended to display some headers in a human readable form:

      >>> decode_header("Some subject")
      'Some subject'
      >>> decode_header("=?ISO-8859-15?Q?D=E9buter_en_Python?=")
      'Débuter en Python'
      >>> decode_header("Re: =?UTF-8?B?cHJvYmzDqG1lIGRlIG1hdHJpY2U=?=")
      'Re: problème de matrice'