Reorganizations and renamings¶
The standard library¶
The Python standard library has been reorganized in Python 3 to be more consistent and easier to use. All the module names now conform to the style guide for Python code, PEP 8[1], and several modules have been merged.
2to3 contains fixers for all of this, so this section is mostly of interest if you need to support both Python 2 and Python 3 without 2to3 conversion.
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 and urllib.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 exception module. 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 the string module. You can use them either on string instances or from the str 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 the float 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 using getattr 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 |