New submission from João Sebastião de Oliveira Bueno: There is an specific Python behavior on object instantiation that is "expected" but not explicit, even for avanced users:
When a custom class defines `__init__` with extra parameters, but do not overrides `__new__`, it simply works. But if `__new__`is defined it has to match `__init__`s signature. This behavior is not documented anywhere. I could found this issue was discussed in this thread earlier this year, starting with this e-mail: https://mail.python.org/pipermail/python-list/2016-March/704013.html I propose the following paragraph from a follow up e-mail by "eryksun at gmail.com" to be added to the description of "__new__" in the Data Model documentation page: """ [The implementation] knows whether a type overrides the __new__ or __init__ methods. You're expected to consume additional arguments in this case. However, excess arguments are ignored in object.__new__ if a type overrides __init__ without overriding __new__ (i.e. your second example). Excess arguments are also ignored in object.__init__ if a type overrides __new__ without overriding __init__. """ (Source: https://mail.python.org/pipermail/python-list/2016-March/704024.html) ---------- assignee: docs@python components: Documentation messages: 280633 nosy: João.Sebastião.de.Oliveira.Bueno, docs@python priority: normal severity: normal status: open title: Explain in the "Data Model" document why arguments to __init__ are ok when __new__ is not defined type: enhancement versions: Python 3.6 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue28672> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
