mib added inline comments.
================
Comment at: lldb/examples/python/crashlog.py:434
except CrashLogFormatException:
- return TextCrashLogParser(debugger, path, verbose).parse()
+ return object().__new__(TextCrashLogParser)
----------------
kastiglione wrote:
> kastiglione wrote:
> > mib wrote:
> > > JDevlieghere wrote:
> > > > kastiglione wrote:
> > > > > mib wrote:
> > > > > > JDevlieghere wrote:
> > > > > > > mib wrote:
> > > > > > > > kastiglione wrote:
> > > > > > > > > I have not seen the `object().__new__(SomeClass)` syntax. Why
> > > > > > > > > is it being used for `TextCrashLogParser` but not
> > > > > > > > > `JSONCrashLogParser`? Also, `__new__` is a static method,
> > > > > > > > > could it be `object.__new__(...)`? Or is there a subtly that
> > > > > > > > > requires an `object` instance? Somewhat related, would it be
> > > > > > > > > better to say `super().__new__(...)`?
> > > > > > > > >
> > > > > > > > > Also: one class construction explicitly forwards the
> > > > > > > > > arguments, the other does not. Is there a reason both aren't
> > > > > > > > > implicit (or both explicit)?
> > > > > > > > As you know, python class are implicitly derived from the
> > > > > > > > `object` type, making `object.__new__` and `super().__new__`
> > > > > > > > pretty much the same thing.
> > > > > > > >
> > > > > > > > In this specific case, both the `TextCrashLogParser` and
> > > > > > > > `JSONCrashLogParser` inherits from the `CrashLogParser` class,
> > > > > > > > so `JSONCrashLogParser` will just inherits
> > > > > > > > `CrashLogParser.__new__` implementation if we don't override
> > > > > > > > it, which creates a recursive loop.
> > > > > > > > That's why I'm calling the `__new__` method specifying the
> > > > > > > > class.
> > > > > > > What's the advantage of this over this compared to a factory
> > > > > > > method? Seems like this could be:
> > > > > > >
> > > > > > > ```
> > > > > > > def create(debugger, path, verbose)
> > > > > > > try:
> > > > > > > return JSONCrashLogParser(debugger, path, verbose)
> > > > > > > except CrashLogFormatException:
> > > > > > > return TextCrashLogParser(debugger, path, verbose)
> > > > > > > ```
> > > > > > If we make a factory, then users could still call `__init__` on
> > > > > > `CrashLogParser` and create a bogus object. With this approach,
> > > > > > they're forced to instantiate a CrashLogParser like any another
> > > > > > object.
> > > > > `CrashLogParser.__init__` could raise an exception. With intricacy of
> > > > > this approach, maybe it's better to use a factor method combined with
> > > > > an exception if the base class `__init__` is called.
> > > > +1, or maybe `abc` provide a capability to achieve the same?
> > > IMHO, having to call an arbitrary-called method (`create/make/...`) to
> > > instantiate an object and having the `__init__` raise an exception
> > > introduces more intricacies in the usage of this class, compared to what
> > > I'm doing.
> > >
> > > I prefer to keep it this way since it's more natural / safe to use. If
> > > the implementation exercises some python internal features, that's fine
> > > because that shouldn't matter to the user.
> > Only after discussing it with you, and reading python docs, do I understand
> > why this code is the way it is. Future editors, including us, could forget
> > some details, which isn't great for maintainability.
> >
> > You mention the user, are there external users of this class hierarchy? Or
> > are these classes internal to crashlog.py? If the latter, then the
> > simplified interface seems hypothetical. If there are external users, how
> > many are they? I am trying to get a sense for what is gained by the
> > avoiding a factory method.
> here's an idea that may simplify things:
>
> instead of embedding validation inside `JSONCrashLogParser.__new__`, have a
> static/class method for validation. Then, the base class can decide which
> subclass by calling the validation method. This means the subclasses don't
> need to override `__new__`. Ex:
>
> ```
> class Base:
> def __new__(cls, i: int):
> if Sub1.is_valid(i):
> return object.__new__(Sub1)
> else:
> return object.__new__(Sub2)
>
> def __init__(self, i: int):
> print("Base", i)
>
> class Sub1(Base):
> @staticmethod
> def is_valid(i: int):
> return i == 1234
>
> def __init__(self, i: int):
> super().__init__(i)
> print("Sub1", i)
>
> class Sub2(Base):
> def __init__(self, i: int):
> super().__init__(i)
> print("Sub2", i)
> ```
@JDevlieghere might be able to give more details on our users but `crashlog.py`
could be imported in other python script, and from what he told me, we have
some internal users that rely on it.
I don't have any strong opinion wrt your suggestion, I'll try it out and update
the patch if that works well. Thanks @kastiglione !
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D131085/new/
https://reviews.llvm.org/D131085
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