# 12 New, Improved, and Deprecated Modules

As usual, Python's standard library received a number of enhancements and bug fixes. Here's a partial list of the most notable changes, sorted alphabetically by module name. Consult the Misc/NEWS file in the source tree for a more complete list of changes, or look through the CVS logs for all the details.

- The `asyncore` module's `loop()` function now has a count parameter that lets you perform a limited number of passes through the polling loop. The default is still to loop forever.

- The `base64` module now has more complete RFC 3548 support for Base64, Base32, and Base16 encoding and decoding, including optional case folding and optional alternative alphabets. (Contributed by Barry Warsaw.)

- The `bisect` module now has an underlying C implementation for improved performance. (Contributed by Dmitry Vasiliev.)

- The CJKCodecs collections of East Asian codecs, maintained by Hye-Shik Chang, was integrated into 2.4. The new encodings are:

  - Chinese (PRC): gb2312, gbk, gb18030, big5hkscs, hz
  - Chinese (ROC): big5, cp950
  - Japanese: cp932, euc-jis-2004, euc-jp, euc-jisx0213, iso-2022-jp, iso-2022-jp-1, iso-2022-jp-2, iso-2022-jp-3, iso-2022-jp-ext, iso-2022-jp-2004, shift-jis, shift-jisx0213, shift-jis-2004
  - Korean: cp949, euc-kr, johab, iso-2022-kr

- Some other new encodings were added: HP Roman8, ISO_8859-11, ISO_8859-16, PCTP-154, and TIS-620.

- The UTF-8 and UTF-16 codecs now cope better with receiving partial input. Previously the `StreamReader` class would try to read more data, making it impossible to resume decoding from the stream. The `read()` method will now return as much data as it can and future calls will resume decoding where previous ones left off. (Implemented by Walter Dörwald.)

- There is a new `collections` module for various specialized collection datatypes. Currently it contains just one type, `deque`, a double-ended queue that supports efficiently adding and removing elements from either end:

      >>> from collections import deque
      >>> d = deque('ghi')        # make a new deque with three items
      >>> d.append('j')           # add a new entry to the right side
      >>> d.appendleft('f')       # add a new entry to the left side
      >>> d                       # show the representation of the deque
      deque(['f', 'g', 'h', 'i', 'j'])
      >>> d.pop()                 # return and remove the rightmost item
      'j'
      >>> d.popleft()             # return and remove the leftmost item
      'f'
      >>> list(d)                 # list the contents of the deque
      ['g', 'h', 'i']
      >>> 'h' in d                # search the deque
      True

  Several modules, such as the `Queue` and `threading` modules, now take advantage of `collections.deque` for improved performance. (Contributed by Raymond Hettinger.)

- The `ConfigParser` classes have been enhanced slightly. The `read()` method now returns a list of the files that were successfully parsed, and the `set()` method raises `TypeError` if passed a value argument that isn't a string. (Contributed by John Belmonte and David Goodger.)

- The `curses` module now supports the ncurses extension `use_default_colors()`. On platforms where the terminal supports transparency, this makes it possible to use a transparent background. (Contributed by Jörg Lehmann.)

- The `difflib` module now includes an `HtmlDiff` class that creates an HTML table showing a side by side comparison of two versions of a text. (Contributed by Dan Gass.)

- The `email` package was updated to version 3.0, which dropped various deprecated APIs and removes support for Python versions earlier than 2.3. The 3.0 version of the package uses a new incremental parser for MIME messages, available in the `email.FeedParser` module. The new parser doesn't require reading the entire message into memory, and doesn't throw exceptions if a message is malformed; instead it records any problems in the `defect` attribute of the message. (Developed by Anthony Baxter, Barry Warsaw, Thomas Wouters, and others.)

- The `heapq` module has been converted to C. The resulting tenfold improvement in speed makes the module suitable for handling high volumes of data. In addition, the module has two new functions `nlargest()` and `nsmallest()` that use heaps to find the N largest or smallest values in a dataset without the expense of a full sort. (Contributed by Raymond Hettinger.)

- The `httplib` module now contains constants for HTTP status codes defined in various HTTP-related RFC documents. Constants have names such as `OK`, `CREATED`, `CONTINUE`, and `MOVED_PERMANENTLY`; use pydoc to get a full list. (Contributed by Andrew Eland.)

- The `imaplib` module now supports IMAP's THREAD command (contributed by Yves Dionne) and new `deleteacl()` and `myrights()` methods (contributed by Arnaud Mazin).

- The `itertools` module gained a `groupby(iterable[, func])` function. iterable is something that can be iterated over to return a stream of elements, and the optional func parameter is a function that takes an element and returns a key value; if omitted, the key is simply the element itself. `groupby()` then groups the elements into subsequences which have matching values of the key, and returns a series of 2-tuples containing the key value and an iterator over the subsequence.

  Here's an example to make this clearer. The key function simply returns whether a number is even or odd, so the result of `groupby()` is to return consecutive runs of odd or even numbers.

      >>> import itertools
      >>> L = [2, 4, 6, 7, 8, 9, 11, 12, 14]
      >>> for key_val, it in itertools.groupby(L, lambda x: x % 2):
      ...    print key_val, list(it)
      ...
      0 [2, 4, 6]
      1 [7]
      0 [8]
      1 [9, 11]
      0 [12, 14]
      >>>

  `groupby()` is typically used with sorted input. The logic for `groupby()` is similar to the Unix `uniq` filter which makes it handy for eliminating, counting, or identifying duplicate elements:

      >>> word = 'abracadabra'
      >>> letters = sorted(word)   # Turn string into a sorted list of letters
      >>> letters
      ['a', 'a', 'a', 'a', 'a', 'b', 'b', 'c', 'd', 'r', 'r']
      >>> for k, g in itertools.groupby(letters):
      ...    print k, list(g)
      ...
      a ['a', 'a', 'a', 'a', 'a']
      b ['b', 'b']
      c ['c']
      d ['d']
      r ['r', 'r']
      >>> # List unique letters
      >>> [k for k, g in groupby(letters)]
      ['a', 'b', 'c', 'd', 'r']
      >>> # Count letter occurrences
      >>> [(k, len(list(g))) for k, g in groupby(letters)]
      [('a', 5), ('b', 2), ('c', 1), ('d', 1), ('r', 2)]

  (Contributed by Hye-Shik Chang.)

- `itertools` also gained a function named `tee(iterator, N)` that returns N independent iterators that replicate iterator. If N is omitted, the default is 2.

      >>> L = [1,2,3]
      >>> i1, i2 = itertools.tee(L)
      >>> i1,i2
      (<itertools.tee object at 0x402c2080>, <itertools.tee object at 0x402c2090>)
      >>> list(i1)               # Run the first iterator to exhaustion
      [1, 2, 3]
      >>> list(i2)               # Run the second iterator to exhaustion
      [1, 2, 3]
      >

  Note that `tee()` has to keep copies of the values returned by the iterator; in the worst case, it may need to keep all of them. This should therefore be used carefully if the leading iterator can run far ahead of the trailing iterator in a long stream of inputs. If the separation is large, then you might as well use `list()` instead. When the iterators track closely with one another, `tee()` is ideal. Possible applications include bookmarking, windowing, or lookahead iterators. (Contributed by Raymond Hettinger.)

- A number of functions were added to the `locale` module, such as `bind_textdomain_codeset()` to specify a particular encoding and a family of `l*gettext()` functions that return messages in the chosen encoding. (Contributed by Gustavo Niemeyer.)

- Some keyword arguments were added to the `logging` package's `basicConfig` function to simplify log configuration. The default behavior is to log messages to standard error, but various keyword arguments can be specified to log to a particular file, change the logging format, or set the logging level. For example:

      import logging
      logging.basicConfig(filename='/var/log/application.log',
          level=0,  # Log all messages
          format='%(levelname):%(process):%(thread):%(message)')

  Other additions to the `logging` package include a `log(level, msg)` convenience method, as well as a `TimedRotatingFileHandler` class that rotates its log files at a timed interval. The module already had `RotatingFileHandler`, which rotated logs once the file exceeded a certain size. Both classes derive from a new `BaseRotatingHandler` class that can be used to implement other rotating handlers.

  (Changes implemented by Vinay Sajip.)

- The `marshal` module now shares interned strings on unpacking a data structure. This may shrink the size of certain pickle strings, but the primary effect is to make .pyc files significantly smaller. (Contributed by Martin von Loewis.)

- The `nntplib` module's `NNTP` class gained `description()` and `descriptions()` methods to retrieve newsgroup descriptions for a single group or for a range of groups. (Contributed by Jürgen A. Erhard.)

- Two new functions were added to the `operator` module, `attrgetter(attr)` and `itemgetter(index)`. Both functions return callables that take a single argument and return the corresponding attribute or item; these callables make excellent data extractors when used with `map()` or `sorted()`. For example:

      >>> L = [('c', 2), ('d', 1), ('a', 4), ('b', 3)]
      >>> map(operator.itemgetter(0), L)
      ['c', 'd', 'a', 'b']
      >>> map(operator.itemgetter(1), L)
      [2, 1, 4, 3]
      >>> sorted(L, key=operator.itemgetter(1)) # Sort list by second tuple item
      [('d', 1), ('c', 2), ('b', 3), ('a', 4)]

  (Contributed by Raymond Hettinger.)

- The `optparse` module was updated in various ways. The module now passes its messages through `gettext.gettext()`, making it possible to internationalize Optik's help and error messages. Help messages for options can now include the string `'%default'`, which will be replaced by the option's default value. (Contributed by Greg Ward.)

- The long-term plan is to deprecate the `rfc822` module in some future Python release in favor of the `email` package. To this end, the `email.Utils.formatdate()` function has been changed to make it usable as a replacement for `rfc822.formatdate()`. You may want to write new e-mail processing code with this in mind. (Change implemented by Anthony Baxter.)

- A new `urandom(n)` function was added to the `os` module, returning a string containing n bytes of random data. This function provides access to platform-specific sources of randomness such as /dev/urandom on Linux or the Windows CryptoAPI. (Contributed by Trevor Perrin.)

- Another new function: `os.path.lexists(path)` returns true if the file specified by path exists, whether or not it's a symbolic link. This differs from the existing `os.path.exists(path)` function, which returns false if path is a symlink that points to a destination that doesn't exist. (Contributed by Beni Cherniavsky.)

- A new `getsid()` function was added to the `posix` module that underlies the `os` module. (Contributed by J. Raynor.)

- The `poplib` module now supports POP over SSL. (Contributed by Hector Urtubia.)

- The `profile` module can now profile C extension functions. (Contributed by Nick Bastin.)

- The `random` module has a new method called `getrandbits(N)` that returns a long integer N bits in length. The existing `randrange()` method now uses `getrandbits()` where appropriate, making generation of arbitrarily large random numbers more efficient. (Contributed by Raymond Hettinger.)

- The regular expression language accepted by the `re` module was extended with simple conditional expressions, written as `(?(group)A|B)`. group is either a numeric group ID or a group name defined with `(?P<group>...)` earlier in the expression. If the specified group matched, the regular expression pattern A will be tested against the string; if the group didn't match, the pattern B will be used instead. (Contributed by Gustavo Niemeyer.)

- The `re` module is also no longer recursive, thanks to a massive amount of work by Gustavo Niemeyer. In a recursive regular expression engine, certain patterns result in a large amount of C stack space being consumed, and it was possible to overflow the stack. For example, if you matched a 30000-byte string of "`a`" characters against the expression `(a|b)+`, one stack frame was consumed per character. Python 2.3 tried to check for stack overflow and raise a `RuntimeError` exception, but certain patterns could sidestep the checking and if you were unlucky Python could segfault. Python 2.4's regular expression engine can match this pattern without problems.

- A new `socketpair()` function, returning a pair of connected sockets, was added to the `socket` module. (Contributed by Dave Cole.)

- The `sys.exitfunc()` function has been deprecated. Code should be using the existing `atexit` module, which correctly handles calling multiple exit functions. Eventually `sys.exitfunc()` will become a purely internal interface, accessed only by `atexit`.

- The `tarfile` module now generates GNU-format tar files by default. (Contributed by Lars Gustaebel.)

- The `threading` module now has an elegantly simple way to support thread-local data. The module contains a `local` class whose attribute values are local to different threads.

      import threading

      data = threading.local()
      data.number = 42
      data.url = ('www.python.org', 80)

  Other threads can assign and retrieve their own values for the `number` and `url` attributes. You can subclass `local` to initialize attributes or to add methods. (Contributed by Jim Fulton.)

- The `timeit` module now automatically disables periodic garbarge collection during the timing loop. This change makes consecutive timings more comparable. (Contributed by Raymond Hettinger.)

- The `weakref` module now supports a wider variety of objects including Python functions, class instances, sets, frozensets, deques, arrays, files, sockets, and regular expression pattern objects. (Contributed by Raymond Hettinger.)

- The `xmlrpclib` module now supports a multi-call extension for transmitting multiple XML-RPC calls in a single HTTP operation. (Contributed by Brian Quinlan.)

- The `mpz`, `rotor`, and `xreadlines` modules have been removed.

## 12.1 cookielib

The `cookielib` library supports client-side handling for HTTP cookies, mirroring the `Cookie` module's server-side cookie support. Cookies are stored in cookie jars; the library transparently stores cookies offered by the web server in the cookie jar, and fetches the cookie from the jar when connecting to the server. As in web browsers, policy objects control whether cookies are accepted or not.

In order to store cookies across sessions, two implementations of cookie jars are provided: one that stores cookies in the Netscape format so applications can use the Mozilla or Lynx cookie files, and one that stores cookies in the same format as the Perl libwww library.

`urllib2` has been changed to interact with `cookielib`: `HTTPCookieProcessor` manages a cookie jar that is used when accessing URLs.

This module was contributed by John J. Lee.

## 12.2 doctest

The `doctest` module underwent considerable refactoring thanks to Edward Loper and Tim Peters. Testing can still be as simple as running `doctest.testmod()`, but the refactorings allow customizing the module's operation in various ways

The new `DocTestFinder` class extracts the tests from a given object's docstrings:

    def f (x, y):
        """>>> f(2,2)
    4
    >>> f(3,2)
    6
        """
        return x*y

    finder = doctest.DocTestFinder()

    # Get list of DocTest instances
    tests = finder.find(f)

The new `DocTestRunner` class then runs individual tests and can produce a summary of the results:

    runner = doctest.DocTestRunner()
    for t in tests:
        tried, failed = runner.run(t)

    runner.summarize(verbose=1)

The above example produces the following output:

    1 items passed all tests:
       2 tests in f
    2 tests in 1 items.
    2 passed and 0 failed.
    Test passed.

`DocTestRunner` uses an instance of the `OutputChecker` class to compare the expected output with the actual output. This class takes a number of different flags that customize its behaviour; ambitious users can also write a completely new subclass of `OutputChecker`.

The default output checker provides a number of handy features. For example, with the `doctest.ELLIPSIS` option flag, an ellipsis ("`...`") in the expected output matches any substring, making it easier to accommodate outputs that vary in minor ways:

    def o (n):
        """>>> o(1)
    <__main__.C instance at 0x...>
    >>>
    """

Another special string, "`<BLANKLINE>`", matches a blank line:

    def p (n):
        """>>> p(1)
    <BLANKLINE>
    >>>
    """

Another new capability is producing a diff-style display of the output by specifying the `doctest.REPORT_UDIFF` (unified diffs), `doctest.REPORT_CDIFF` (context diffs), or `doctest.REPORT_NDIFF` (delta-style) option flags. For example:

    def g (n):
        """>>> g(4)
    here
    is
    a
    lengthy
    >>>"""
        L = 'here is a rather lengthy list of words'.split()
        for word in L[:n]:
            print word

Running the above function's tests with `doctest.REPORT_UDIFF` specified, you get the following output:

    **********************************************************************
    File ``t.py'', line 15, in g
    Failed example:
        g(4)
    Differences (unified diff with -expected +actual):
        @@ -2,3 +2,3 @@
         is
         a
        -lengthy
        +rather
    **********************************************************************