Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail From: Peter Otten <__peter__@web.de> Newsgroups: comp.lang.python Subject: Re: What use of these _ prefix members? Date: Tue, 12 Jan 2016 15:52:18 +0100 Organization: None Lines: 50 Message-ID: References: <4ee5810e-abe9-4c4b-9ebd-d989b5c2b341@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Trace: news.uni-berlin.de lBcnN8S0Cnl0UJklLMqtbA5RIOSzggJTvp62975a8sKw== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.002 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'source,': 0.04; '*args,': 0.07; 'override': 0.07; '*args': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'subclasses': 0.09; 'subject:members': 0.09; 'def': 0.13; 'instead.': 0.15; 'distinct': 0.16; 'inheritance': 0.16; 'received:80.91.229.3': 0.16; 'received:dip0.t-ipconnect.de': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'received:t-ipconnect.de': 0.16; 'wrote:': 0.16; 'looked': 0.16; 'arguments': 0.22; 'class,': 0.22; 'own.': 0.22; 'pass': 0.22; 'decide': 0.23; 'header:User-Agent:1': 0.26; 'header:X-Complaints- To:1': 0.26; 'sense': 0.26; 'question': 0.27; 'turns': 0.27; 'function': 0.28; 'actual': 0.28; 'invoke': 0.29; 'code': 0.30; 'option': 0.31; 'posting': 0.32; 'class': 0.33; 'foo': 0.33; 'though.': 0.33; 'except': 0.34; 'that,': 0.34; 'generic': 0.35; 'robert': 0.35; 'subject:use': 0.35; 'something': 0.35; 'expected': 0.35; 'sometimes': 0.35; 'should': 0.36; 'instead': 0.36; 'to:addr:python-list': 0.36; 'subject:?': 0.36; 'subject:: ': 0.37; 'method': 0.37; 'received:org': 0.37; 'doing': 0.38; "won't": 0.38; 'someone': 0.38; 'mean': 0.38; 'rather': 0.39; 'to:addr:python.org': 0.40; 'received:de': 0.40; 'software': 0.40; 'sample': 0.63; '>>>>>': 0.66; 'elsewhere': 0.66; 'endorsement.': 0.84; 'enforced': 0.84; 'otten': 0.84; 'private.': 0.84; 'x):': 0.84; 'approach.': 0.91 X-Injected-Via-Gmane: http://gmane.org/ X-Gmane-NNTP-Posting-Host: p57bd8ad4.dip0.t-ipconnect.de User-Agent: KNode/4.13.3 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.20+ Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Xref: csiph.com comp.lang.python:101545 Someone else posting as "me" wrote: > On 2016-01-10, Peter Otten <__peter__@web.de> wrote: >>>>> class Derived(Base): >> ... def _init(self, x): >> ... super()._init(x) >> ... print("do something else with", x) >> ... >>>>> Derived(42) >> do something with 42 >> do something else with 42 >><__main__.Derived object at 0x7f8e6b3e9b70> >> > > I think you are doing inheritance wrong. If by "you" you mean "me" -- the above sample is an illustration of the pattern I expected to see elsewhere in the software Robert was quoting, not an endorsement. I have now looked into the hmmlearn source, and it turns out that _init() is invoked by the fit() method rather than the initializer. But... > AFAIK you should call directly the __init__() of the parent class, and > pass *args and **kwargs instead. you sometimes want to break initialisation or any other method into distinct steps that don't make sense stand-alone: class Foo: def method(...) self._one(...) self._two(...) self._three(...) That way subclasses have the option to override only _two() instead of method() and users of Foo won't try to invoke _two(...) on its own. I think this is a good approach. What arguments you need to accept and/or pass on is a question that you can decide depending on the actual use-case. I use *args, **kwargs only if function is very generic because it makes code hard to follow. > Except for that, yes, the _init would be conventionally private. Not > enforced by name mangling though.