Supporting Python 3(支持python3)——结构调整和重命名

结构调整和重命名

标准库The standard library

为了一致性和使用起来更容易，Python的标准库在Python 3已经被调整结构了。所有的模块名现在符合Python代码的风格引导，PEP 8[1]；并且一些模块被合并了。

2to3包含的固定器可以处理所有的这些，所以这个章节更多的是引起你是否需要不用2to3转换同时支持Python 2和Python 3的兴趣。

The six module[2] has support for most of the standard library reorganization. You can import the reorganized modules from six.moves:

>>> from six.moves import cStringIO

In Python 2 this will be equivalent to:

>>> from cStringIO import StringIO

While in Python 3 this will be equivalent to:

>>> from io import StringIO

If you want to support Python 2 and Python 3 without conversion and you don’t want to use the six module, this is also very easy. You just try to import from one location, catch the error and then import from the other location. It doesn’t matter of you put the Python 3 location first or last, both works equally well:

>>> try:...     from io import StringIO... except ImportError:...     from cStringIO import StringIO

This table contains the renamings and reorganizations of the standard library, except for the urllib, urllib2 and urlparse reorganization, which has a separate table:

Python 2 name	Python 3 name	six name
anydbm	dbm
BaseHTTPServer	http.server	BaseHTTPServer
__builtin__	builtins	builtins
CGIHTTPServer	http.server	CGIHTTPServer
ConfigParser	configparser	configparser
copy_reg	copyreg	copyreg
cPickle	pickle	cPickle
cProfile	profile
cStringIO.StringIO	io.StringIO	cStringIO
Cookie	http.cookies	http_cookies
cookielib	http.cookiejar	http_cookiejar
dbhash	dbm.bsd
dbm	dbm.ndbm
dumbdb	dbm.dumb
Dialog	tkinter.dialog	tkinter_dialog
DocXMLRPCServer	xmlrpc.server
FileDialog	tkinter.FileDialog	tkinter_filedialog
FixTk	tkinter._fix
gdbm	dbm.gnu
htmlentitydefs	html.entities	html_entities
HTMLParser	html.parser	html_parser
httplib	http.client	http_client
markupbase	_markupbase
Queue	queue	queue
repr	reprlib	reprlib
robotparser	urllib.robotparser	urllib_robotparser
ScrolledText	tkinter.scolledtext	tkinter_scrolledtext
SimpleDialog	tkinter.simpledialog	tkinter_simpledialog
SimpleHTTPServer	http.server	SimpleHTTPServer
SimpleXMLRPCServer	xmlrpc.server
StringIO.StringIO	io.StringIO
SocketServer	socketserver	socketserver
test.test_support	test.support	tkinter
Tkinter	tkinter	tkinter
Tix	tkinter.tix	tkinter_tix
Tkconstants	tkinter.constants	tkinter_constants
tkColorChooser	tkinter.colorchooser	tkinter_colorchooser
tkCommonDialog	tkinter.commondialog	tkinter_commondialog
Tkdnd	tkinter.dnd	tkinter_dnd
tkFileDialog	tkinter.filedialog	tkinter_tkfiledialog
tkFont	tkinter.font	tkinter_font
tkMessageBox	tkinter.messagebox	tkinter_messagebox
tkSimpleDialog	tkinter.simpledialog	tkinter_tksimpledialog
turtle	tkinter.turtle
UserList	collections
UserString	collections
whichdb	dbm
_winreg	winreg	winreg
xmlrpclib	xmlrpc.client

urllib, urllib2 and urlparse

The three modules urllib, urllib2 and urlparse has been reorganized into three new modules, urllib.request, urllib.parse andurllib.error. Since there is no six support for these renames you have to use the try/except technique above.

Python 2 name	Moved to
urllib._urlopener	urllib.request
urllib.ContentTooShortError	urllib.error
urllib.FancyURLOpener	urllib.request
urllib.pathname2url	urllib.request
urllib.quote	urllib.parse
urllib.quote_plus	urllib.parse
urllib.splitattr	urllib.parse
urllib.splithost	urllib.parse
urllib.splitnport	urllib.parse
urllib.splitpasswd	urllib.parse
urllib.splitport	urllib.parse
urllib.splitquery	urllib.parse
urllib.splittag	urllib.parse
urllib.splittype	urllib.parse
urllib.splituser	urllib.parse
urllib.splitvalue	urllib.parse
urllib.unquote	urllib.parse
urllib.unquote_plus	urllib.parse
urllib.urlcleanup	urllib.request
urllib.urlencode	urllib.parse
urllib.urlopen	urllib.request
urllib.URLOpener	urllib.request
urllib.urlretrieve	urllib.request
urllib2.AbstractBasicAuthHandler	urllib.request
urllib2.AbstractDigestAuthHandler	urllib.request
urllib2.BaseHandler	urllib.request
urllib2.build_opener	urllib.request
urllib2.CacheFTPHandler	urllib.request
urllib2.FileHandler	urllib.request
urllib2.FTPHandler	urllib.request
urllib2.HTTPBasicAuthHandler	urllib.request
urllib2.HTTPCookieProcessor	urllib.request
urllib2.HTTPDefaultErrorHandler	urllib.request
urllib2.HTTPDigestAuthHandler	urllib.request
urllib2.HTTPError	urllib.request
urllib2.HTTPHandler	urllib.request
urllib2.HTTPPasswordMgr	urllib.request
urllib2.HTTPPasswordMgrWithDefaultRealm	urllib.request
urllib2.HTTPRedirectHandler	urllib.request
urllib2.HTTPSHandler	urllib.request
urllib2.install_opener	urllib.request
urllib2.OpenerDirector	urllib.request
urllib2.ProxyBasicAuthHandler	urllib.request
urllib2.ProxyDigestAuthHandler	urllib.request
urllib2.ProxyHandler	urllib.request
urllib2.Request	urllib.request
urllib2.UnknownHandler	urllib.request
urllib2.URLError	urllib.request
urllib2.urlopen	urllib.request
urlparse.parse_qs	urllib.parse
urlparse.parse_qsl	urllib.parse
urlparse.urldefrag	urllib.parse
urlparse.urljoin	urllib.parse
urlparse.urlparse	urllib.parse
urlparse.urlsplit	urllib.parse
urlparse.urlunparse	urllib.parse
urlparse.urlunsplit	urllib.parse

Removed modules

Some of the standard library modules have been dropped. One is UserDict, but some of the classes have replacements that are almost, but not quite completely compatible. See Replacing UserDict for more information on that.

Most of the other modules that have been dropped are modules that have long been supplanted by other, improved modules, or modules that are specific to platforms that is no longer supported. Fittingly, and exception to this rule is the exception module. It contains a hierarchy of exceptions, but all of them are also built-ins, so you never need to import anything from the exceptionmodule. It has therefore been removed from Python 3 completely.

Except for the modules specific for Solaris, IRIX and Mac OS 9, this is the list of modules that has been removed in Python 3:

Module name	Comment
audiodev
Bastion
bsddb185	Supplanted by bsddb3
bsddb3	Available on the CheeseShop
Canvas
cfmfile
cl
commands
compiler
dircache
dl	Supplanted by ctypes
exception	See above
fpformat
htmllib	Supplanted html.parser
ihooks
imageop
imputil
linuxaudiodev	Supplanted by ossaudiodev
md5	Supplanted by hashlib
mhlib
mimetools	Supplanted by email
MimeWriter	Supplanted by email
mimify	Supplanted by email
multifile	Supplanted by email
mutex
new
popen2	Supplanted by subprocess
posixfile
pure
rexec
rfc822	Supplanted by email
sha	Supplanted by hashlib
sgmllib
sre	Supplanted by re
stat	Supplanted by os.stat()
stringold
sunaudio
sv
test.testall
thread	Supplanted by threading
timing
toaiff
user

Moved builtins

There are also a couple of builtin functions that have been moved to standard library modules. You handle them in a similar way, by trying to import them from the Python 3 location and if this fails you just do nothing:

>>> try:...     from imp import reload... except ImportError:...     pass

The moved builtins are:

Python 2 name	Python 3 name	six name
intern()	sys.intern()
reduce()	functools.reduce()	reduce
reload()	imp.reload()	reload_module

string module removals

Several functions have existed both in the string module and as methods on the str type and instances. These have now been removed from thestring module. You can use them either on string instances or from thestr type itself. So what in Python 2 could be written:

>>> import string>>> string.upper('Dinsdale!')'DINSDALE!'

Should now be written in one of the following ways:

>>> 'Dinsdale!'.upper()'DINSDALE!'>>> str.upper('Dinsdale!')'DINSDALE!'

The first way of doing it is the most common one, but moving to the second way can be done with a simple search and replace.

The removed functions are capitalize(), center(), count(),expandtabs(), find(), index(), join(), ljust(),lower(), lstrip(), maketrans(), replace(), rfind(),rindex(), rjust(), rsplit(), rstrip(), split(),strip(), swapcase(), translate(), upper() and zfill().

In addition the functions atof(), atoi() and atol() has been removed, and have been replaced with passing the string value into thefloat and int constructors. Since these functions have been deprecated since Python 2.0 it’s highly unlikely that you actually use them.

Function and method attribute renamings

Many of the special attribute names on functions and methods were named before it was decided that Python should use the “double underscore” method for special names used by Python. They   have been renamed in Python 3.

The easiest way of handling this if you are not using 2to3 is to define a variable with the attribute name depending on the Python version and usinggetattr to access the attribute. This doesn’t work in the case of the renaming of im_class, though, so there you need a function to fetch the result:

>>> import sys>>> if sys.version_info < (3,):...     defaults_attr = 'func_defaults'...     get_method_class = lambda x: x.im_class... else:...     defaults_attr = '__defaults__'...     get_method_class = lambda x: x.__self__.__class__>>> class Test(object):...     def hasdefaults(a=1, b=2):...         pass>>> method = Test().hasdefaults>>> getattr(method, defaults_attr)(1, 2)>>> get_method_class(method)<class 'Test'>

Six has  defined functions to retrieve the most common attribute names:

Python 2 name	Python 3 name	six function
func_closure	__closure__
func_doc	__doc__
func_globals	__globals__
func_name	__name__
func_defaults	__defaults__	get_function_defaults()
func_code	__code__	get_function_code()
func_dict	__dict__
im_func	__func__	get_method_function()
im_self	__self__	get_method_self()
im_class	__self__.__class__

Footnotes

[1]	http://www.python.org/dev/peps/pep-0008/

[2]	http://pypi.python.org/pypi/six

本文地址：http://my.oschina.net/soarwilldo/blog/538255

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原文http://python3porting.com/differences.html

引导页Supporting Python 3:（支持Python3）：深入指南

目录Supporting Python 3（支持Python 3）——目录