[issue19438] Where is NoneType in Python 3?
New submission from mpb: types.NoneType seems to have disappeared in Python 3. This is probably intentional, but I cannot figure out how to test if a variable is of type NoneType in Python 3. Specifically, I want to write: assert type (v) in ( bytes, types.NoneType ) Yes, I could write: assert v is None or type (v) is bytes But the first assert statement is easier to read (IMO). Here are links to various Python 3 documentation about None: [1] http://docs.python.org/3/library/stdtypes.html#index-2 [2] http://docs.python.org/3/library/constants.html#None Link [2] says: "None The sole value of the type NoneType." However, NoneType is not listed in the Python 3 documentation index. (As compared with the Python 2 index, where NoneType is listed.) [3] http://docs.python.org/3/library/types.html If NoneType is gone in Python 3, mention of NoneType should probably be removed from link [2]. If NoneType is present in Python 3, the docs (presumably at least one of the above links, and hopefully also the index) should tell me how to use it. Here is another link: [4] http://docs.python.org/3/library/stdtypes.html#bltin-type-objects "The standard module types defines names for all standard built-in types." (Except <class 'NoneType'> ???) None is a built-in constant. It has a type. If None's type is not considered to be a "standard built-in type", then IMO this is surprising(!!) and should be documented somewhere (for example, at link [4], and possibly elsewhere as well.) Thanks! ---------- assignee: docs@python components: Documentation messages: 201666 nosy: docs@python, mpb priority: normal severity: normal status: open title: Where is NoneType in Python 3? versions: Python 3.3 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue19438> _______________________________________
Christian Heimes added the comment: How about: type(v) in (bytes, type(None)) or: isinstance(v, (bytes, type(None)) or: v is None or type(v) is bytes or: v is None or isinstance(v, bytes) ---------- nosy: +christian.heimes _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue19438> _______________________________________
mpb added the comment: Of your 4 suggestions, I mentioned #3 and #4 in my post. They are less readable, IMO. 1 and 2 are nicer, but both have an "extra" set of nested parenthesis. While I appreciate the suggestions, I submitted this as a documentation bug, because I think I should be able to find these suggestions somewhere in the Python 3 documentation, at one (or more) of the links I included in my bug report. Also, the Python 3 documentation does mention NoneType, and if NoneType is not part of Python 3, I claim this is an error in the documentation. And then, there is my personal favorite work-around: NoneType = type (None) # only needed once assert type (v) in ( bytes, NoneType ) Or (perhaps more confusingly, LOL!): none = type (None) assert type (v) in ( bytes, none ) isinstance is more confusing because it takes two arguments. Whenever I use it I have to think, "isinstance" vs "instanceof", which is Python, which is Java? (And I haven't used Java seriously in years!) And then I have to think about the order of the arguments (v, cls) vs (cls, v). type is just simpler than isinstance. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue19438> _______________________________________
R. David Murray added the comment: See http://www.python.org/dev/peps/pep-0294/ for some background on this. The unexpected thing is actually that the types module still exists at all in Python3 :) That said, its documentation could, indeed, use some improvement to address this kind of question. Searching the python-dev email list for 'NoneType removal types module" turns up some interesting posts, back in the 2.3 days...basically, type(None) is the One True Way to get NoneType :) ---------- nosy: +r.david.murray _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue19438> _______________________________________
mpb added the comment: Regarding http://www.python.org/dev/peps/pep-0294/ ... Complete removal of the types module makes more sense to me than letting types continue, but removing NoneType from it! If type(None) is the one_true_way, then the docs should say that, possibly in multiple locations. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue19438> _______________________________________
Changes by Christian Heimes <lists@cheimes.de>: ---------- nosy: -christian.heimes priority: normal -> low versions: +Python 3.4 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue19438> _______________________________________
Change by Andrés Delfino <adelfino@gmail.com>: ---------- keywords: +patch nosy: +adelfino nosy_count: 3.0 -> 4.0 pull_requests: +21235 stage: -> patch review pull_request: https://github.com/python/cpython/pull/22161 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue19438> _______________________________________
Raymond Hettinger <raymond.hettinger@gmail.com> added the comment: I would support adding NoneType back to the types module. Am not sure why it was ever removed. It has a much reason to exists as types.FunctionType which is a clear, well-named short-cut for "type(lambda :None)". ---------- nosy: +rhettinger _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue19438> _______________________________________
Andrés Delfino <adelfino@gmail.com> added the comment: types.NoneType was removed here: https://github.com/python/cpython/commit/c9543e42330e5f339d6419eba6a8c5a61a3... The thing of adding NoneType to types that is somewhat unpleasing to me is that it's named exactly as the actual type. Seems confusing. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue19438> _______________________________________
Raymond Hettinger <raymond.hettinger@gmail.com> added the comment: Thanks for the link. It looks like NoneType got inadvertently caught up in the sweep of names that had direct synonyms. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue19438> _______________________________________
Andrés Delfino <adelfino@gmail.com> added the comment: ammar2 found this mail mentioning the changes in that commit https://mail.python.org/pipermail/python-dev/2007-November/075386.html "I've removed the 'new' module from py3k and also removed a lot of types from the 'types' module in py3k. It only contains types that aren't easily available through builtins." ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue19438> _______________________________________
Andrés Delfino <adelfino@gmail.com> added the comment: As per https://github.com/python/cpython/pull/22336 I believe this issue can be closed now. My PR is not relevant to the problem stated by OP, so I'm "unlinking" it. ---------- resolution: -> fixed stage: patch review -> resolved status: open -> closed _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue19438> _______________________________________
participants (5)
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Andrés Delfino -
Christian Heimes
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mpb
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R. David Murray
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Raymond Hettinger