Python 3.3 的新功能 ¶

from errno import ENOENT, EACCES, EPERM
try:
    with open("document.txt") as f:
        content = f.read()
except IOError as err:
    if err.errno == ENOENT:
        print("document.txt file is missing")
    elif err.errno in (EACCES, EPERM):
        print("You are not allowed to read document.txt")
    else:
        raise
					

try:
    with open("document.txt") as f:
        content = f.read()
except FileNotFoundError:
    print("document.txt file is missing")
except PermissionError:
    print("You are not allowed to read document.txt")
					

>>> def g(x):
...     yield from range(x, 0, -1)
...     yield from range(x)
...
>>> list(g(5))
[5, 4, 3, 2, 1, 0, 1, 2, 3, 4]
					

>>> def accumulate():
...     tally = 0
...     while 1:
...         next = yield
...         if next is None:
...             return tally
...         tally += next
...
>>> def gather_tallies(tallies):
...     while 1:
...         tally = yield from accumulate()
...         tallies.append(tally)
...
>>> tallies = []
>>> acc = gather_tallies(tallies)
>>> next(acc) # Ensure the accumulator is ready to accept values
>>> for i in range(4):
...     acc.send(i)
...
>>> acc.send(None) # Finish the first tally
>>> for i in range(5):
...     acc.send(i)
...
>>> acc.send(None) # Finish the second tally
>>> tallies
[6, 10]
					

>>> class D:
...     def __init__(self, extra):
...         self._extra_attributes = extra
...     def __getattr__(self, attr):
...         try:
...             return self._extra_attributes[attr]
...         except KeyError:
...             raise AttributeError(attr) from None
...
>>> D({}).x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 8, in __getattr__
AttributeError: x
						

>>> class C:
...     def __init__(self, extra):
...         self._extra_attributes = extra
...     def __getattr__(self, attr):
...         try:
...             return self._extra_attributes[attr]
...         except KeyError:
...             raise AttributeError(attr)
...
>>> C({}).x
Traceback (most recent call last):
  File "<stdin>", line 6, in __getattr__
KeyError: 'x'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 8, in __getattr__
AttributeError: x
						

>>> try:
...     D({}).x
... except AttributeError as exc:
...     print(repr(exc.__context__))
...
KeyError('x',)
						

>>> class C:
...     def meth(self):
...         pass
>>> C.meth.__name__
'meth'
>>> C.meth.__qualname__
'C.meth'
						

>>> class C:
...     class D:
...         def meth(self):
...             pass
...
>>> C.D.__name__
'D'
>>> C.D.__qualname__
'C.D'
>>> C.D.meth.__name__
'meth'
>>> C.D.meth.__qualname__
'C.D.meth'
						

>>> def outer():
...     def inner():
...         pass
...     return inner
...
>>> outer().__name__
'inner'
>>> outer().__qualname__
'outer.<locals>.inner'
						

>>> str(C.D)
"<class '__main__.C.D'>"
>>> str(C.D.meth)
'<function C.D.meth at 0x7f46b9fe31e0>'
						

$ python -q -X faulthandler
>>> import ctypes
>>> ctypes.string_at(0)
Fatal Python error: Segmentation fault
Current thread 0x00007fb899f39700:
  File "/home/python/cpython/Lib/ctypes/__init__.py", line 486 in string_at
  File "<stdin>", line 1 in <module>
Segmentation fault
						

$ ./python -q
>>> import codecs
>>> encoder = codecs.getincrementalencoder('hz')('strict')
>>> b''.join(encoder.encode(x) for x in '\u52ff\u65bd\u65bc\u4eba\u3002 Bye.')
b'~{NpJ)l6HK!#~} Bye.'
						

API 变化 ¶

• The C module has the following context limits, depending on the machine architecture:

  	32 位	64-bit
  MAX_PREC	425000000	999999999999999999
  MAX_EMAX	425000000	999999999999999999
  MIN_EMIN	-425000000	-999999999999999999

• In the context templates ( DefaultContext , BasicContext and ExtendedContext ) the magnitude of Emax and Emin 已变成 999999 .

• The Decimal constructor in decimal.py does not observe the context limits and converts values with arbitrary exponents or precision exactly. Since the C version has internal limits, the following scheme is used: If possible, values are converted exactly, otherwise InvalidOperation is raised and the result is NaN. In the latter case it is always possible to use create_decimal() in order to obtain a rounded or inexact value.

• The power function in decimal.py is always correctly-rounded. In the C version, it is defined in terms of the correctly-rounded exp() and ln() functions, but the final result is only “almost always correctly rounded”.

• In the C version, the context dictionary containing the signals is a MutableMapping . For speed reasons, flags and traps always refer to the same MutableMapping that the context was initialized with. If a new signal dictionary is assigned, flags and traps are updated with the new values, but they do not reference the RHS dictionary.

• Pickling a Context produces a different output in order to have a common interchange format for the Python and C versions.

• The order of arguments in the Context constructor has been changed to match the order displayed by repr() .

• The watchexp parameter in the quantize() 方法被弃用。

email ¶

Policy Framework ¶

The email package now has a policy framework. A Policy is an object with several methods and properties that control how the email package behaves. The primary policy for Python 3.3 is the Compat32 policy, which provides backward compatibility with the email package in Python 3.2. A policy can be specified when an email message is parsed by a parser , or when a Message object is created, or when an email is serialized using a generator . Unless overridden, a policy passed to a parser is inherited by all the Message object and sub-objects created by the parser . By default a generator will use the policy of the Message object it is serializing. The default policy is compat32 .

The minimum set of controls implemented by all policy objects are:

A new policy instance, with new settings, is created using the clone() method of policy objects. clone takes any of the above controls as keyword arguments. Any control not specified in the call retains its default value. Thus you can create a policy that uses \r\n linesep characters like this:

mypolicy = compat32.clone(linesep='\r\n')
					

Policies can be used to make the generation of messages in the format needed by your application simpler. Instead of having to remember to specify linesep='\r\n' in all the places you call a generator , you can specify it once, when you set the policy used by the parser 或 Message , whichever your program uses to create Message objects. On the other hand, if you need to generate messages in multiple forms, you can still specify the parameters in the appropriate generator call. Or you can have custom policy instances for your different cases, and pass those in when you create the generator .

Provisional Policy with New Header API ¶

While the policy framework is worthwhile all by itself, the main motivation for introducing it is to allow the creation of new policies that implement new features for the email package in a way that maintains backward compatibility for those who do not use the new policies. Because the new policies introduce a new API, we are releasing them in Python 3.3 as a provisional policy . Backwards incompatible changes (up to and including removal of the code) may occur if deemed necessary by the core developers.

The new policies are instances of EmailPolicy , and add the following additional controls:

The header_factory is the key to the new features provided by the new policies. When one of the new policies is used, any header retrieved from a Message object is an object produced by the header_factory , and any time you set a header on a Message it becomes an object produced by header_factory . All such header objects have a name attribute equal to the header name. Address and Date headers have additional attributes that give you access to the parsed data of the header. This means you can now do things like this:

>>> m = Message(policy=SMTP)
>>> m['To'] = 'Éric <foo@example.com>'
>>> m['to']
'Éric <foo@example.com>'
>>> m['to'].addresses
(Address(display_name='Éric', username='foo', domain='example.com'),)
>>> m['to'].addresses[0].username
'foo'
>>> m['to'].addresses[0].display_name
'Éric'
>>> m['Date'] = email.utils.localtime()
>>> m['Date'].datetime
datetime.datetime(2012, 5, 25, 21, 39, 24, 465484, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000), 'EDT'))
>>> m['Date']
'Fri, 25 May 2012 21:44:27 -0400'
>>> print(m)
To: =?utf-8?q?=C3=89ric?= <foo@example.com>
Date: Fri, 25 May 2012 21:44:27 -0400
					

You will note that the unicode display name is automatically encoded as utf-8 when the message is serialized, but that when the header is accessed directly, you get the unicode version. This eliminates any need to deal with the email.header decode_header() or make_header() 函数。

You can also create addresses from parts:

>>> m['cc'] = [Group('pals', [Address('Bob', 'bob', 'example.com'),
...                           Address('Sally', 'sally', 'example.com')]),
...            Address('Bonzo', addr_spec='bonz@laugh.com')]
>>> print(m)
To: =?utf-8?q?=C3=89ric?= <foo@example.com>
Date: Fri, 25 May 2012 21:44:27 -0400
cc: pals: Bob <bob@example.com>, Sally <sally@example.com>;, Bonzo <bonz@laugh.com>
					

Decoding to unicode is done automatically:

>>> m2 = message_from_string(str(m))
>>> m2['to']
'Éric <foo@example.com>'
					

When you parse a message, you can use the addresses and groups attributes of the header objects to access the groups and individual addresses:

>>> m2['cc'].addresses
(Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com'), Address(display_name='Bonzo', username='bonz', domain='laugh.com'))
>>> m2['cc'].groups
(Group(display_name='pals', addresses=(Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com')), Group(display_name=None, addresses=(Address(display_name='Bonzo', username='bonz', domain='laugh.com'),))
					

In summary, if you use one of the new policies, header manipulation works the way it ought to: your application works with unicode strings, and the email package transparently encodes and decodes the unicode to and from the RFC standard Content Transfer Encodings.

Other API Changes ¶

New BytesHeaderParser , added to the parser module to complement HeaderParser and complete the Bytes API.

New utility functions:

• format_datetime() : given a datetime , produce a string formatted for use in an email header.
• parsedate_to_datetime() : given a date string from an email header, convert it into an aware datetime , or a naive datetime if the offset is -0000 .
• localtime() : With no argument, returns the current local time as an aware datetime using the local timezone . Given an aware datetime , converts it into an aware datetime 使用 local timezone .

ftplib ¶

• ftplib.FTP 现在接受 source_address keyword argument to specify the (host, port) to use as the source address in the bind call when creating the outgoing socket. (Contributed by Giampaolo Rodolà in issue 8594 )。
• The FTP_TLS class now provides a new ccc() function to revert control channel back to plaintext. This can be useful to take advantage of firewalls that know how to handle NAT with non-secure FTP without opening fixed ports. (Contributed by Giampaolo Rodolà in issue 12139 )。
• 添加 ftplib.FTP.mlsd() method which provides a parsable directory listing format and deprecates ftplib.FTP.nlst() and ftplib.FTP.dir() . (Contributed by Giampaolo Rodolà in issue 11072 )。

functools ¶

The functools.lru_cache() decorator now accepts a typed keyword argument (that defaults to False to ensure that it caches values of different types that compare equal in separate cache slots. (Contributed by Raymond Hettinger in issue 13227 )。

gc ¶

It is now possible to register callbacks invoked by the garbage collector before and after collection using the new callbacks 列表。

hmac ¶

新的 compare_digest() function has been added to prevent side channel attacks on digests through timing analysis. (Contributed by Nick Coghlan and Christian Heimes in issue 15061 )。

http ¶

http.server.BaseHTTPRequestHandler now buffers the headers and writes them all at once when end_headers() is called. A new method flush_headers() can be used to directly manage when the accumlated headers are sent. (Contributed by Andrew Schaaf in issue 3709 )。

http.server now produces valid HTML 4.01 strict output. (Contributed by Ezio Melotti in issue 13295 )。

http.client.HTTPResponse now has a readinto() method, which means it can be used as an io.RawIOBase class. (Contributed by John Kuhn in issue 13464 )。

html ¶

html.parser.HTMLParser is now able to parse broken markup without raising errors, therefore the strict argument of the constructor and the HTMLParseError exception are now deprecated. The ability to parse broken markup is the result of a number of bug fixes that are also available on the latest bug fix releases of Python 2.7/3.2. (Contributed by Ezio Melotti in issue 15114 ，和 issue 14538 , issue 13993 , issue 13960 , issue 13358 , issue 1745761 , issue 755670 , issue 13357 , issue 12629 , issue 1200313 , issue 670664 , issue 13273 , issue 12888 , issue 7311 )。

新的 html5 dictionary that maps HTML5 named character references to the equivalent Unicode character(s) (e.g. html5['gt;'] == '>' ) has been added to the html.entities module. The dictionary is now also used by HTMLParser . (Contributed by Ezio Melotti in issue 11113 and issue 15156 )。

imaplib ¶

The IMAP4_SSL constructor now accepts an SSLContext parameter to control parameters of the secure channel.

(Contributed by Sijin Joseph in issue 8808 )。

inspect ¶

新的 getclosurevars() function has been added. This function reports the current binding of all names referenced from the function body and where those names were resolved, making it easier to verify correct internal state when testing code that relies on stateful closures.

(Contributed by Meador Inge and Nick Coghlan in issue 13062 )。

新的 getgeneratorlocals() function has been added. This function reports the current binding of local variables in the generator’s stack frame, making it easier to verify correct internal state when testing generators.

(Contributed by Meador Inge in issue 15153 )。

io ¶

The open() function has a new 'x' mode that can be used to exclusively create a new file, and raise a FileExistsError if the file already exists. It is based on the C11 ‘x’ mode to fopen().

(Contributed by David Townshend in issue 12760 )。

The constructor of the TextIOWrapper class has a new write_through optional argument. If write_through is True ，调用 write() are guaranteed not to be buffered: any data written on the TextIOWrapper object is immediately handled to its underlying binary buffer.

itertools ¶

accumulate() now takes an optional func argument for providing a user-supplied binary function.

logging ¶

The basicConfig() function now supports an optional handlers argument taking an iterable of handlers to be added to the root logger.

A class level attribute append_nul has been added to SysLogHandler to allow control of the appending of the NUL ( \000 ) byte to syslog records, since for some deamons it is required while for others it is passed through to the log.

math ¶

The math module has a new function, log2() , which returns the base-2 logarithm of x .

(Written by Mark Dickinson in issue 11888 )。

mmap ¶

The read() method is now more compatible with other file-like objects: if the argument is omitted or specified as None , it returns the bytes from the current file position to the end of the mapping. (Contributed by Petri Lehtinen in issue 12021 )。

multiprocessing ¶

新的 multiprocessing.connection.wait() function allows to poll multiple objects (such as connections, sockets and pipes) with a timeout. (Contributed by Richard Oudkerk in issue 12328 )。

multiprocessing.Connection objects can now be transferred over multiprocessing connections. (Contributed by Richard Oudkerk in issue 4892 )。

multiprocessing.Process 现在接受 daemon keyword argument to override the default behavior of inheriting the daemon flag from the parent process ( issue 6064 ).

New attribute multiprocessing.Process.sentinel allows a program to wait on multiple Process objects at one time using the appropriate OS primitives (for example, select on posix systems).

New methods multiprocessing.pool.Pool.starmap() and starmap_async() 提供 itertools.starmap() equivalents to the existing multiprocessing.pool.Pool.map() and map_async() functions. (Contributed by Hynek Schlawack in issue 12708 )。

nntplib ¶

The nntplib.NNTP class now supports the context management protocol to unconditionally consume socket.error exceptions and to close the NNTP connection when done:

>>> 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')
>>>
					

(Contributed by Giampaolo Rodolà in issue 9795 )。

os ¶

• The os module has a new pipe2() function that makes it possible to create a pipe with O_CLOEXEC or O_NONBLOCK flags set atomically. This is especially useful to avoid race conditions in multi-threaded programs.

• The os module has a new sendfile() function which provides an efficient “zero-copy” way for copying data from one file (or socket) descriptor to another. The phrase “zero-copy” refers to the fact that all of the copying of data between the two descriptors is done entirely by the kernel, with no copying of data into userspace buffers. sendfile() can be used to efficiently copy data from a file on disk to a network socket, e.g. for downloading a file.

  (Patch submitted by Ross Lagerwall and Giampaolo Rodolà in issue 10882 )。

• To avoid race conditions like symlink attacks and issues with temporary files and directories, it is more reliable (and also faster) to manipulate file descriptors instead of file names. Python 3.3 enhances existing functions and introduces new functions to work on file descriptors ( issue 4761 , issue 10755 and issue 14626 ).

  • The os module has a new fwalk() function similar to walk() except that it also yields file descriptors referring to the directories visited. This is especially useful to avoid symlink races.
  • The following functions get new optional dir_fd ( paths relative to directory descriptors ) and/or follow_symlinks ( not following symlinks ): access() , chflags() , chmod() , chown() , link() , lstat() , mkdir() , mkfifo() , mknod() , open() , readlink() , remove() , rename() , replace() , rmdir() , stat() , symlink() , unlink() , utime() . Platform support for using these parameters can be checked via the sets os.supports_dir_fd and os.supports_follows_symlinks .
  • The following functions now support a file descriptor for their path argument: chdir() , chmod() , chown() , execve() , listdir() , pathconf() , exists() , stat() , statvfs() , utime() . Platform support for this can be checked via the os.supports_fd set.

• access() accepts an effective_ids keyword argument to turn on using the effective uid/gid rather than the real uid/gid in the access check. Platform support for this can be checked via the supports_effective_ids set.

• The os module has two new functions: getpriority() and setpriority() . They can be used to get or set process niceness/priority in a fashion similar to os.nice() but extended to all processes instead of just the current one.

  (Patch submitted by Giampaolo Rodolà in issue 10784 )。

• 新的 os.replace() function allows cross-platform renaming of a file with overwriting the destination. With os.rename() , an existing destination file is overwritten under POSIX, but raises an error under Windows. (Contributed by Antoine Pitrou in issue 8828 )。

• The stat family of functions ( stat() , fstat() ，和 lstat() ) now support reading a file’s timestamps with nanosecond precision. Symmetrically, utime() can now write file timestamps with nanosecond precision. (Contributed by Larry Hastings in issue 14127 )。

• 新的 os.get_terminal_size() function queries the size of the terminal attached to a file descriptor. See also shutil.get_terminal_size() . (Contributed by Zbigniew Jędrzejewski-Szmek in issue 13609 )。

• New functions to support Linux extended attributes ( issue 12720 ): getxattr() , listxattr() , removexattr() , setxattr() .
• New interface to the scheduler. These functions control how a process is allocated CPU time by the operating system. New functions: sched_get_priority_max() , sched_get_priority_min() , sched_getaffinity() , sched_getparam() , sched_getscheduler() , sched_rr_get_interval() , sched_setaffinity() , sched_setparam() , sched_setscheduler() , sched_yield() ,
• New functions to control the file system:
  • posix_fadvise() : Announces an intention to access data in a specific pattern thus allowing the kernel to make optimizations.
  • posix_fallocate() : Ensures that enough disk space is allocated for a file.
  • sync() : Force write of everything to disk.
• Additional new posix functions:
  • lockf() : Apply, test or remove a POSIX lock on an open file descriptor.
  • pread() : Read from a file descriptor at an offset, the file offset remains unchanged.
  • pwrite() : Write to a file descriptor from an offset, leaving the file offset unchanged.
  • readv() : Read from a file descriptor into a number of writable buffers.
  • truncate() : Truncate the file corresponding to path , so that it is at most length 字节大小。
  • waitid() : Wait for the completion of one or more child processes.
  • writev() : Write the contents of buffers to a file descriptor, where buffers is an arbitrary sequence of buffers.
  • getgrouplist() ( issue 9344 ): Return list of group ids that specified user belongs to.
• times() and uname() : Return type changed from a tuple to a tuple-like object with named attributes.
• Some platforms now support additional constants for the lseek() function, such as os.SEEK_HOLE and os.SEEK_DATA .
• New constants RTLD_LAZY , RTLD_NOW , RTLD_GLOBAL , RTLD_LOCAL , RTLD_NODELETE , RTLD_NOLOAD ，和 RTLD_DEEPBIND are available on platforms that support them. These are for use with the sys.setdlopenflags() function, and supersede the similar constants defined in ctypes and DLFCN . (Contributed by Victor Stinner in issue 13226 )。
• os.symlink() now accepts (and ignores) the target_is_directory keyword argument on non-Windows platforms, to ease cross-platform support.

pdb ¶

Tab-completion is now available not only for command names, but also their arguments. For example, for the break command, function and file names are completed.

(Contributed by Georg Brandl in issue 14210 )

pickle ¶

pickle.Pickler objects now have an optional dispatch_table attribute allowing to set per-pickler reduction functions.

(Contributed by Richard Oudkerk in issue 14166 )。

pydoc ¶

The Tk GUI and the serve() function have been removed from the pydoc 模块： pydoc -g and serve() have been deprecated in Python 3.2.

re ¶

str regular expressions now support \u and \U 转义。

(Contributed by Serhiy Storchaka in issue 3665 )。

sched ¶

• run() 现在接受 blocking parameter which when set to False makes the method execute the scheduled events due to expire soonest (if any) and then return immediately. This is useful in case you want to use the scheduler in non-blocking applications. (Contributed by Giampaolo Rodolà in issue 13449 )。
• scheduler class can now be safely used in multi-threaded environments. (Contributed by Josiah Carlson and Giampaolo Rodolà in issue 8684 )。
• timefunc and delayfunct parameters of scheduler class constructor are now optional and defaults to time.time() and time.sleep() respectively. (Contributed by Chris Clark in issue 13245 )。
• enter() and enterabs() argument parameter is now optional. (Contributed by Chris Clark in issue 13245 )。
• enter() and enterabs() now accept a kwargs parameter. (Contributed by Chris Clark in issue 13245 )。

select ¶

Solaris and derivative platforms have a new class select.devpoll for high performance asynchronous sockets via /dev/poll . (Contributed by Jesús Cea Avión in issue 6397 )。

shlex ¶

The previously undocumented helper function quote 从 pipes modules has been moved to the shlex module and documented. quote() properly escapes all characters in a string that might be otherwise given special meaning by the shell.

shutil ¶

• New functions:
  • disk_usage() : provides total, used and free disk space statistics. (Contributed by Giampaolo Rodolà in issue 12442 )。
  • chown() : allows one to change user and/or group of the given path also specifying the user/group names and not only their numeric ids. (Contributed by Sandro Tosi in issue 12191 )。
  • shutil.get_terminal_size() : returns the size of the terminal window to which the interpreter is attached. (Contributed by Zbigniew Jędrzejewski-Szmek in issue 13609 )。
• copy2() and copystat() now preserve file timestamps with nanosecond precision on platforms that support it. They also preserve file “extended attributes” on Linux. (Contributed by Larry Hastings in issue 14127 and issue 15238 )。
• Several functions now take an optional symlinks argument: when that parameter is true, symlinks aren’t dereferenced and the operation instead acts on the symlink itself (or creates one, if relevant). (Contributed by Hynek Schlawack in issue 12715 )。
• When copying files to a different file system, move() now handles symlinks the way the posix mv command does, recreating the symlink rather than copying the target file contents. (Contributed by Jonathan Niehof in issue 9993 )。 move() now also returns the dst argument as its result.
• rmtree() is now resistant to symlink attacks on platforms which support the new dir_fd parameter in os.open() and os.unlink() . (Contributed by Martin von Löwis and Hynek Schlawack in issue 4489 )。

signal ¶

• The signal module has new functions:
  • pthread_sigmask() : fetch and/or change the signal mask of the calling thread (Contributed by Jean-Paul Calderone in issue 8407 );
  • pthread_kill() : send a signal to a thread;
  • sigpending() : examine pending functions;
  • sigwait() : wait a signal;
  • sigwaitinfo() : wait for a signal, returning detailed information about it;
  • sigtimedwait() : like sigwaitinfo() but with a timeout.
• The signal handler writes the signal number as a single byte instead of a nul byte into the wakeup file descriptor. So it is possible to wait more than one signal and know which signals were raised.
• signal.signal() and signal.siginterrupt() raise an OSError, instead of a RuntimeError: OSError has an errno attribute.

smtpd ¶

The smtpd module now supports RFC 5321 (extended SMTP) and RFC 1870 (size extension). Per the standard, these extensions are enabled if and only if the client initiates the session with an EHLO 命令。

(Initial ELHO support by Alberto Trevino. Size extension by Juhana Jauhiainen. Substantial additional work on the patch contributed by Michele Orrù and Dan Boswell. issue 8739 )

smtplib ¶

The SMTP , SMTP_SSL ，和 LMTP classes now accept a source_address keyword argument to specify the (host, port) to use as the source address in the bind call when creating the outgoing socket. (Contributed by Paulo Scardine in issue 11281 )。

SMTP now supports the context management protocol, allowing an SMTP instance to be used in a with statement. (Contributed by Giampaolo Rodolà in issue 11289 )。

The SMTP_SSL constructor and the starttls() method now accept an SSLContext parameter to control parameters of the secure channel. (Contributed by Kasun Herath in issue 8809 )。

socket ¶

• The socket class now exposes additional methods to process ancillary data when supported by the underlying platform:

  • sendmsg()
  • recvmsg()
  • recvmsg_into()

  (Contributed by David Watson in issue 6560 , based on an earlier patch by Heiko Wundram)

• The socket class now supports the PF_CAN protocol family ( http://en.wikipedia.org/wiki/Socketcan ), on Linux ( http://lwn.net/Articles/253425 ).

  (Contributed by Matthias Fuchs, updated by Tiago Gonçalves in issue 10141 )。

• The socket class now supports the PF_RDS protocol family ( http://en.wikipedia.org/wiki/Reliable_Datagram_Sockets and https://oss.oracle.com/projects/rds/ ).

• The socket class now supports the PF_SYSTEM protocol family on OS X. (Contributed by Michael Goderbauer in issue 13777 )。

• New function sethostname() allows the hostname to be set on unix systems if the calling process has sufficient privileges. (Contributed by Ross Lagerwall in issue 10866 )。

socketserver ¶

BaseServer now has an overridable method service_actions() that is called by the serve_forever() method in the service loop. ForkingMixIn now uses this to clean up zombie child processes. (Contributed by Justin Warkentin in issue 11109 )。

sqlite3 ¶

New sqlite3.Connection 方法 set_trace_callback() can be used to capture a trace of all sql commands processed by sqlite. (Contributed by Torsten Landschoff in issue 11688 )。

ssl ¶

• The ssl module has two new random generation functions:

  • RAND_bytes() : generate cryptographically strong pseudo-random bytes.
  • RAND_pseudo_bytes() : generate pseudo-random bytes.

  (Contributed by Victor Stinner in issue 12049 )。

• The ssl module now exposes a finer-grained exception hierarchy in order to make it easier to inspect the various kinds of errors. (Contributed by Antoine Pitrou in issue 11183 )。

• load_cert_chain() 现在接受 password argument to be used if the private key is encrypted. (Contributed by Adam Simpkins in issue 12803 )。

• Diffie-Hellman key exchange, both regular and Elliptic Curve-based, is now supported through the load_dh_params() and set_ecdh_curve() methods. (Contributed by Antoine Pitrou in issue 13626 and issue 13627 )。

• SSL sockets have a new get_channel_binding() method allowing the implementation of certain authentication mechanisms such as SCRAM-SHA-1-PLUS. (Contributed by Jacek Konieczny in issue 12551 )。

• You can query the SSL compression algorithm used by an SSL socket, thanks to its new compression() method. The new attribute OP_NO_COMPRESSION can be used to disable compression. (Contributed by Antoine Pitrou in issue 13634 )。

• Support has been added for the Next Procotol Negotiation extension using the ssl.SSLContext.set_npn_protocols() method. (Contributed by Colin Marc in issue 14204 )。

• SSL errors can now be introspected more easily thanks to library and reason attributes. (Contributed by Antoine Pitrou in issue 14837 )。

• The get_server_certificate() function now supports IPv6. (Contributed by Charles-François Natali in issue 11811 )。

• New attribute OP_CIPHER_SERVER_PREFERENCE allows setting SSLv3 server sockets to use the server’s cipher ordering preference rather than the client’s ( issue 13635 ).

stat ¶

The undocumented tarfile.filemode function has been moved to stat.filemode() . It can be used to convert a file’s mode to a string of the form ‘-rwxrwxrwx’.

(Contributed by Giampaolo Rodolà in issue 14807 )。

struct ¶

The struct module now supports ssize_t and size_t via the new codes n and N , respectively. (Contributed by Antoine Pitrou in issue 3163 )。

subprocess ¶

Command strings can now be bytes objects on posix platforms. (Contributed by Victor Stinner in issue 8513 )。

A new constant DEVNULL allows suppressing output in a platform-independent fashion. (Contributed by Ross Lagerwall in issue 5870 )。

sys ¶

The sys module has a new thread_info 结构序列 holding informations about the thread implementation ( issue 11223 ).

tarfile ¶

tarfile 现在支持 lzma encoding via the lzma module. (Contributed by Lars Gustäbel in issue 5689 )。

tempfile ¶

tempfile.SpooledTemporaryFile ‘s truncate() method now accepts a size parameter. (Contributed by Ryan Kelly in issue 9957 )。

textwrap ¶

The textwrap module has a new indent() that makes it straightforward to add a common prefix to selected lines in a block of text ( issue 13857 ).

threading ¶

threading.Condition , threading.Semaphore , threading.BoundedSemaphore , threading.Event ，和 threading.Timer , all of which used to be factory functions returning a class instance, are now classes and may be subclassed. (Contributed by Éric Araujo in issue 10968 )。

The threading.Thread constructor now accepts a daemon keyword argument to override the default behavior of inheriting the deamon flag value from the parent thread ( issue 6064 ).

The formerly private function _thread.get_ident is now available as the public function threading.get_ident() . This eliminates several cases of direct access to the _thread module in the stdlib. Third party code that used _thread.get_ident should likewise be changed to use the new public interface.

time ¶

The PEP 418 added new functions to the time 模块：

• get_clock_info() : Get information on a clock.
• monotonic() : Monotonic clock (cannot go backward), not affected by system clock updates.
• perf_counter() : Performance counter with the highest available resolution to measure a short duration.
• process_time() : Sum of the system and user CPU time of the current process.

Other new functions:

• clock_getres() , clock_gettime() and clock_settime() functions with CLOCK_xxx 常量。 (Contributed by Victor Stinner in issue 10278 )。

To improve cross platform consistency, sleep() now raises a ValueError when passed a negative sleep value. Previously this was an error on posix, but produced an infinite sleep on Windows.

类型 ¶

Add a new types.MappingProxyType class: Read-only proxy of a mapping. ( issue 14386 )

The new functions types.new_class() and types.prepare_class() provide support for PEP 3115 compliant dynamic type creation. ( issue 14588 )

unittest ¶

assertRaises() , assertRaisesRegex() , assertWarns() ，和 assertWarnsRegex() now accept a keyword argument msg when used as context managers. (Contributed by Ezio Melotti and Winston Ewert in issue 10775 )。

unittest.TestCase.run() now returns the TestResult 对象。

urllib ¶

The Request class, now accepts a 方法 argument used by get_method() to determine what HTTP method should be used. For example, this will send a 'HEAD' 请求：

>>> urlopen(Request('https://www.python.org', method='HEAD'))
					

( issue 1673007 )

webbrowser ¶

The webbrowser module supports more “browsers”: Google Chrome (named chrome , chromium , chrome-browser or chromium-browser depending on the version and operating system), and the generic launchers xdg-open , from the FreeDesktop.org project, and gvfs-open , which is the default URI handler for GNOME 3. (The former contributed by Arnaud Calmettes in issue 13620 , the latter by Matthias Klose in issue 14493 )。

xml.etree.ElementTree ¶

The xml.etree.ElementTree module now imports its C accelerator by default; there is no longer a need to explicitly import xml.etree.cElementTree (this module stays for backwards compatibility, but is now deprecated). In addition, the iter family of methods of Element has been optimized (rewritten in C). The module’s documentation has also been greatly improved with added examples and a more detailed reference.

zlib ¶

New attribute zlib.Decompress.eof makes it possible to distinguish between a properly-formed compressed stream and an incomplete or truncated one. (Contributed by Nadeem Vawda in issue 12646 )。

New attribute zlib.ZLIB_RUNTIME_VERSION reports the version string of the underlying zlib library that is loaded at runtime. (Contributed by Torsten Landschoff in issue 12306 )。

优化 ¶

Major performance enhancements have been added:

• Thanks to PEP 393 , some operations on Unicode strings have been optimized:

  • the memory footprint is divided by 2 to 4 depending on the text
  • encode an ASCII string to UTF-8 doesn’t need to encode characters anymore, the UTF-8 representation is shared with the ASCII representation
  • the UTF-8 encoder has been optimized
  • repeating a single ASCII letter and getting a substring of an ASCII string is 4 times faster

• UTF-8 is now 2x to 4x faster. UTF-16 encoding is now up to 10x faster.

  (Contributed by Serhiy Storchaka, issue 14624 , issue 14738 and issue 15026 )。

构建和 C API 变化 ¶

Changes to Python’s build process and to the C API include:

• New PEP 3118 related function:
  • PyMemoryView_FromMemory()
• PEP 393 added new Unicode types, macros and functions:
  • High-level API:
    • PyUnicode_CopyCharacters()
    • PyUnicode_FindChar()
    • PyUnicode_GetLength() , PyUnicode_GET_LENGTH
    • PyUnicode_New()
    • PyUnicode_Substring()
    • PyUnicode_ReadChar() , PyUnicode_WriteChar()
  • Low-level API:
    • Py_UCS1 , Py_UCS2 , Py_UCS4 类型
    • PyASCIIObject and PyCompactUnicodeObject structures
    • PyUnicode_READY
    • PyUnicode_FromKindAndData()
    • PyUnicode_AsUCS4() , PyUnicode_AsUCS4Copy()
    • PyUnicode_DATA , PyUnicode_1BYTE_DATA , PyUnicode_2BYTE_DATA , PyUnicode_4BYTE_DATA
    • PyUnicode_KIND with PyUnicode_Kind 枚举： PyUnicode_WCHAR_KIND , PyUnicode_1BYTE_KIND , PyUnicode_2BYTE_KIND , PyUnicode_4BYTE_KIND
    • PyUnicode_READ , PyUnicode_READ_CHAR , PyUnicode_WRITE
    • PyUnicode_MAX_CHAR_VALUE
• PyArg_ParseTuple 现在接受 bytearray 为 c format ( issue 12380 ).

弃用 ¶

Unsupported Operating Systems ¶

OS/2 and VMS are no longer supported due to the lack of a maintainer.

Windows 2000 and Windows platforms which set COMSPEC to command.com are no longer supported due to maintenance burden.

OSF support, which was deprecated in 3.2, has been completely removed.

弃用 Python 模块、函数和方法 ¶

• Passing a non-empty string to object.__format__() is deprecated, and will produce a TypeError in Python 3.4 ( issue 9856 ).
• The unicode_internal codec has been deprecated because of the PEP 393 , use UTF-8, UTF-16 ( utf-16-le or utf-16-be ), or UTF-32 ( utf-32-le or utf-32-be )
• ftplib.FTP.nlst() and ftplib.FTP.dir() : use ftplib.FTP.mlsd()
• platform.popen() ：使用 subprocess module. Check especially the 替换较旧函数采用 subprocess 模块 section ( issue 11377 ).
• issue 13374 : The Windows bytes API has been deprecated in the os module. Use Unicode filenames, instead of bytes filenames, to not depend on the ANSI code page anymore and to support any filename.
• issue 13988 ： xml.etree.cElementTree module is deprecated. The accelerator is used automatically whenever available.
• The behaviour of time.clock() depends on the platform: use the new time.perf_counter() or time.process_time() function instead, depending on your requirements, to have a well defined behaviour.
• The os.stat_float_times() function is deprecated.
• abc 模块：
  • abc.abstractproperty has been deprecated, use property with abc.abstractmethod() 代替。
  • abc.abstractclassmethod has been deprecated, use classmethod with abc.abstractmethod() 代替。
  • abc.abstractstaticmethod has been deprecated, use staticmethod with abc.abstractmethod() 代替。
• importlib 包：
  • importlib.abc.SourceLoader.path_mtime() is now deprecated in favour of importlib.abc.SourceLoader.path_stats() as bytecode files now store both the modification time and size of the source file the bytecode file was compiled from.

弃用函数和 C API 类型 ¶

The Py_UNICODE has been deprecated by PEP 393 and will be removed in Python 4. All functions using this type are deprecated:

Unicode functions and methods using Py_UNICODE and Py_UNICODE* types:

• PyUnicode_FromUnicode : use PyUnicode_FromWideChar() or PyUnicode_FromKindAndData()
• PyUnicode_AS_UNICODE , PyUnicode_AsUnicode() , PyUnicode_AsUnicodeAndSize() : use PyUnicode_AsWideCharString()
• PyUnicode_AS_DATA : use PyUnicode_DATA with PyUnicode_READ and PyUnicode_WRITE
• PyUnicode_GET_SIZE , PyUnicode_GetSize() : use PyUnicode_GET_LENGTH or PyUnicode_GetLength()
• PyUnicode_GET_DATA_SIZE : use PyUnicode_GET_LENGTH(str) * PyUnicode_KIND(str) (only work on ready strings)
• PyUnicode_AsUnicodeCopy() : use PyUnicode_AsUCS4Copy() or PyUnicode_AsWideCharString()
• PyUnicode_GetMax()

Functions and macros manipulating Py_UNICODE* strings:

• Py_UNICODE_strlen : use PyUnicode_GetLength() or PyUnicode_GET_LENGTH
• Py_UNICODE_strcat : use PyUnicode_CopyCharacters() or PyUnicode_FromFormat()
• Py_UNICODE_strcpy , Py_UNICODE_strncpy , Py_UNICODE_COPY : use PyUnicode_CopyCharacters() or PyUnicode_Substring()
• Py_UNICODE_strcmp : use PyUnicode_Compare()
• Py_UNICODE_strncmp : use PyUnicode_Tailmatch()
• Py_UNICODE_strchr , Py_UNICODE_strrchr : use PyUnicode_FindChar()
• Py_UNICODE_FILL : use PyUnicode_Fill()
• Py_UNICODE_MATCH

Encoders:

• PyUnicode_Encode() : use PyUnicode_AsEncodedObject()
• PyUnicode_EncodeUTF7()
• PyUnicode_EncodeUTF8() : use PyUnicode_AsUTF8() or PyUnicode_AsUTF8String()
• PyUnicode_EncodeUTF32()
• PyUnicode_EncodeUTF16()
• PyUnicode_EncodeUnicodeEscape:() 使用 PyUnicode_AsUnicodeEscapeString()
• PyUnicode_EncodeRawUnicodeEscape:() 使用 PyUnicode_AsRawUnicodeEscapeString()
• PyUnicode_EncodeLatin1() : use PyUnicode_AsLatin1String()
• PyUnicode_EncodeASCII() : use PyUnicode_AsASCIIString()
• PyUnicode_EncodeCharmap()
• PyUnicode_TranslateCharmap()
• PyUnicode_EncodeMBCS() : use PyUnicode_AsMBCSString() or PyUnicode_EncodeCodePage() (with CP_ACP code_page)
• PyUnicode_EncodeDecimal() , PyUnicode_TransformDecimalToASCII()

Deprecated features ¶

The array 模块的 'u' format code is now deprecated and will be removed in Python 4 together with the rest of the ( Py_UNICODE ) API.

移植到 Python 3.3 ¶

This section lists previously described changes and other bugfixes that may require changes to your code.

移植 Python 代码 ¶

• Hash randomization is enabled by default. Set the PYTHONHASHSEED 环境变量到 0 to disable hash randomization. See also the object.__hash__() 方法。
• issue 12326 : On Linux, sys.platform doesn’t contain the major version anymore. It is now always ‘linux’, instead of ‘linux2’ or ‘linux3’ depending on the Linux version used to build Python. Replace sys.platform == ‘linux2’ with sys.platform.startswith(‘linux’), or directly sys.platform == ‘linux’ if you don’t need to support older Python versions.
• issue 13847 , issue 14180 : time and datetime : OverflowError is now raised instead of ValueError 若 timestamp is out of range. OSError is now raised if C functions gmtime() or localtime() failed.
• The default finders used by import now utilize a cache of what is contained within a specific directory. If you create a Python source file or sourceless bytecode file, make sure to call importlib.invalidate_caches() to clear out the cache for the finders to notice the new file.
• ImportError now uses the full name of the module that was attempted to be imported. Doctests that check ImportErrors’ message will need to be updated to use the full name of the module instead of just the tail of the 名称。
• The index 自变量对于 __import__() now defaults to 0 instead of -1 and no longer support negative values. It was an oversight when PEP 328 was implemented that the default value remained -1. If you need to continue to perform a relative import followed by an absolute import, then perform the relative import using an index of 1, followed by another import using an index of 0. It is preferred, though, that you use importlib.import_module() rather than call __import__() 直接。
• __import__() no longer allows one to use an index value other than 0 for top-level modules. E.g. __import__('sys', level=1) is now an error.
• 因为 sys.meta_path and sys.path_hooks now have finders on them by default, you will most likely want to use list.insert() 代替 of list.append() to add to those lists.
• 因为 None is now inserted into sys.path_importer_cache , if you are clearing out entries in the dictionary of paths that do not have a finder, you will need to remove keys paired with values of None and imp.NullImporter to be backwards-compatible. This will lead to extra overhead on older versions of Python that re-insert None into sys.path_importer_cache where it repesents the use of implicit finders, but semantically it should not change anything.
• importlib.abc.Finder no longer specifies a find_module() abstract method that must be implemented. If you were relying on subclasses to implement that method, make sure to check for the method’s existence first. You will probably want to check for find_loader() first, though, in the case of working with 路径条目查找器 .
• pkgutil has been converted to use importlib internally. This eliminates many edge cases where the old behaviour of the PEP 302 import emulation failed to match the behaviour of the real import system. The import emulation itself is still present, but is now deprecated. The pkgutil.iter_importers() and pkgutil.walk_packages() 函数 special case the standard import hooks so they are still supported even though they do not provide the non-standard iter_modules() 方法。
• A longstanding RFC-compliance bug ( issue 1079 ) in the parsing done by email.header.decode_header() has been fixed. Code that uses the standard idiom to convert encoded headers into unicode ( str(make_header(decode_header(h)) ) will see no change, but code that looks at the individual tuples returned by decode_header will see that whitespace that precedes or follows ASCII sections is now included in the ASCII section. Code that builds headers using make_header should also continue to work without change, since make_header continues to add whitespace between ASCII and non- ASCII sections if it is not already present in the input strings.
• email.utils.formataddr() now does the correct content transfer encoding when passed non- ASCII display names. Any code that depended on the previous buggy behavior that preserved the non- ASCII unicode in the formatted output string will need to be changed ( issue 1690608 ).
• poplib.POP3.quit() may now raise protocol errors like all other poplib methods. Code that assumes quit does not raise poplib.error_proto errors may need to be changed if errors on quit are encountered by a particular application ( issue 11291 ).
• The strict 自变量对于 email.parser.Parser , deprecated since Python 2.4, has finally been removed.
• The deprecated method unittest.TestCase.assertSameElements has been removed.
• The deprecated variable time.accept2dyear 已被移除。
• The deprecated Context._clamp attribute has been removed from the decimal module. It was previously replaced by the public attribute clamp 。(见 issue 8540 )。
• The undocumented internal helper class SSLFakeFile has been removed from smtplib , since its functionality has long been provided directly by socket.socket.makefile() .
• Passing a negative value to time.sleep() on Windows now raises an error instead of sleeping forever. It has always raised an error on posix.
• The ast.__version__ constant has been removed. If you need to make decisions affected by the AST version, use sys.version_info to make the decision.
• Code that used to work around the fact that the threading module used factory functions by subclassing the private classes will need to change to subclass the now-public classes.
• The undocumented debugging machinery in the threading module has been removed, simplifying the code. This should have no effect on production code, but is mentioned here in case any application debug frameworks were interacting with it ( issue 13550 ).

Porting C code ¶

• In the course of changes to the buffer API the undocumented smalltable 成员对于 Py_buffer structure has been removed and the layout of the PyMemoryViewObject 已改变。

  All extensions relying on the relevant parts in memoryobject.h or object.h must be rebuilt.

• 由于 PEP 393 ， Py_UNICODE type and all functions using this type are deprecated (but will stay available for at least five years). If you were using low-level Unicode APIs to construct and access unicode objects and you want to benefit of the memory footprint reduction provided by PEP 393, you have to convert your code to the new Unicode API .

  However, if you only have been using high-level functions such as PyUnicode_Concat() , PyUnicode_Join() or PyUnicode_FromFormat() , your code will automatically take advantage of the new unicode representations.

• PyImport_GetMagicNumber() now returns -1 upon failure.

• As a negative value for the level 自变量对于 __import__() is no longer valid, the same now holds for PyImport_ImportModuleLevel() . This also means that the value of level used by PyImport_ImportModuleEx() is now 0 instead of -1.

Building C extensions ¶

• The range of possible file names for C extensions has been narrowed. Very rarely used spellings have been suppressed: under POSIX, files named xxxmodule.so , xxxmodule.abi3.so and xxxmodule.cpython-*.so are no longer recognized as implementing the xxx module. If you had been generating such files, you have to switch to the other spellings (i.e., remove the module string from the file names).

  (implemented in issue 14040 )。

Command Line Switch Changes ¶

• The -Q command-line flag and related artifacts have been removed. Code checking sys.flags.division_warning will need updating.

  ( issue 10998 , contributed by Éric Araujo.)

• 当 python is started with -S , import site will no longer add site-specific paths to the module search paths. In previous versions, it did.

  ( issue 11591 , contributed by Carl Meyer with editions by Éric Araujo.)