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| Python is a mature language, but it hasn't stopped evolving, and there are some issues to consider when coding Python, if you want your code to work with the latest version of Python in five five years from now... See http://www.python.org/peps/pep-3000.html for more information. |
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| = Write Tests = | The future of [[http://www.python.org/peps/pep-3000.html|Python 3000]] is now! As of January 2020 Python 2 will be in EOL (End Of Life) status and receive no further official support. After that date, there will be no further updates nor bugfixes. Since this end-of-life date has been planned for nearly a decade (the first end-of-life date was slated to happen in 2014, and was pushed back to 2020), and nearly all popular libraries have already ported their code, Python 2.x is well on its way out. |
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| Automated testing is generally better than debuging, and is your safety-net for any kind of refatoring, not only when migrating to a newer Python. Use PyUnit (unittest), DocTest or any alternative (see UnitTests) to help you. | [[https://wiki.python.org/moin/FutureProofPython?action=recall&rev=28|Previous page revisions]] have historical information that may be useful in porting or maintaining remaining Python 2 systems. If you need additional support in porting existing 2.x code to 3.x, please see the resources available for [[PortingPythonToPy3k|porting Python 2 code]]. |
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| = True Division = Since the beginning, Python has yielded an integer result when two integers are divided, e.g. 3/2 => 1. While correct if we assume that dividing integers means integer division (the remainder is accessible through the modulo operator %) it's not always obvious to beginners. This behaviour will change in a future Python version, so that a/b with yield a float as a result even if both a and b are integers, and a new floor division operator // will perform integer division. See See http://www.python.org/peps/pep-0238.html '''Use true and floor division in new code''' {{{ from __future__ import division # Enable the new behaviour f = 3/2 # 1.5 i = 3//2 # 1 }}} = New style classes = Currently, there are two kinds of classes in Python. The 'classic' or old style classes, and the new style classes. Old style classes will go away in some future version, and while most code will still work when the default swaps from old style to new style, there are some differences in semantics, and the new style classes have some extra features. See http://www.python.org/doc/newstyle.html '''Use new style classes in new code''' Don't write {{{ class X: pass }}} Write {{{ class X(object): pass }}} = Let all exception classes inherit from Exception = From Python 3.0, all exceptions must be derived from Base''''''Exception, which will be the base class for Keyboard''''''Interrupt, System''''''Exit and Exception from Python 2.5. See http://www.python.org/peps/pep-0352.html '''When defining new exception classes, always inherit (directly or indirectly) from Exception''' {{{ class MyException(Exception): pass }}} = Use parenthesis for Exception argument = The syntax {{{ raise MyException "A nasty error" }}} will be deprecated. Use {{{ raise MyException("A nasty error") }}} instead. = Don't compare uncomparable objects = In the future, x < y and friends (>, <=, >=) will raise an exception instead of an arbitrary result, if type(x) != type(y) unless the types explicitly define the behaviour for these comparisions. = Don't use <> = It's enough with one inequality operator. Almost everybody uses !=. <> will go away. = Don't use `` (backticks) = The `backticks` for repr() will not exist in Python3.0 - Almost everybody use repr(foo), and many don't even know of `foo`. It is also harder to read. = Don't assign to with, as, nonlocal, True and False = They are becoming keywords. = See more = Collin Winter have some tips in: [http://oakwinter.com/code/porting-setuptools-to-py3k/] = More changes in the future? = The following little code might be useful to run when you upgrade to a new Python version. It shows how some new features in Python is getting gradually enabled. (This example is from Python 2.3.) {{{ >>> import __future__ >>> for x in __future__.all_feature_names: ... print x, eval('__future__.'+x) ... nested_scopes _Feature((2, 1, 0, 'beta', 1), (2, 2, 0, 'alpha', 0), 16) generators _Feature((2, 2, 0, 'alpha', 1), (2, 3, 0, 'final', 0), 4096) division _Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192) }}} The second tuple (e.g. (3, 0, 0, 'alpha', 0) for division) shows when a new feature will become the default. |
---- CategoryDocumentation |
The future of Python 3000 is now! As of January 2020 Python 2 will be in EOL (End Of Life) status and receive no further official support. After that date, there will be no further updates nor bugfixes. Since this end-of-life date has been planned for nearly a decade (the first end-of-life date was slated to happen in 2014, and was pushed back to 2020), and nearly all popular libraries have already ported their code, Python 2.x is well on its way out.
Previous page revisions have historical information that may be useful in porting or maintaining remaining Python 2 systems. If you need additional support in porting existing 2.x code to 3.x, please see the resources available for porting Python 2 code.