Python @classmethod were added for this exact reason - Alternative
Contructors.
class Foo(object):
def __init__(self, bar=None, baz=None):
self._bar = bar
self._baz = baz
print 'bar: {}, baz: {}'.format(self._bar, self._baz)
@classmethod
def from_bar(cls, bar):
return cls(bar=bar)
@classmethod
def from_baz(cls, baz):
return cls(baz=baz)
# Default
foo = Foo('default bar', 'default baz')
# bar: default bar, baz: default baz
# From bar
foo_bar = Foo.from_bar('from bar')
# bar: from bar, baz: None
# From baz
foo_baz = Foo.from_baz('from baz')
# bar: None, baz: from baz
- Alok
On Wed, Apr 15, 2020, 10:44 HarshadB <bari.hars...@gmail.com> wrote:
> Hoping for some help with this, I am trying to understand Class
> construction(instantiation before init).
>
> I have a component class which encapsulates a hierarchy of nodes in Maya.
> Instantiated using a mObject as input.
> BaseComponent(mObject)
>
> I want to automate the instance construction of this class based on
> selection, mObjectHandle, string and have created classmethods (as
> alternative constructors) for the same. I wanted to allow initiation just
> by BaseComponent() that will take the selection and avoid
> BaseComponent.some_method as default.
>
> Goal:
> BaseComponent() # Takes selection
> BaseComponent.fromString() # Takes string name of an object in scene
> BaseComponent.fromMObjectHandle() # Takes an mObjectHandle for an object
> in scene
> BaseComponent(mObject) # Takes mObject as default
>
> Currently trying to implement this with __new__. Previously, all the
> "isinstance" checks were done in init which I wanted to simplify.
> I couldn't get it to work exactly how I wanted to, but I did get it to
> work with all four arg input types (selection, str, mObjectHandle, mObject).
>
> Problems:
> - The problem is there's no clear error/warning if the end-user makes a
> mistake.
> - All alternative constructors also pass to the init where I had to put a
> mObject isinstance check for it to work. If possible, I want to remove
> mObject check in init as mObject should be the only one passed to init.
>
> I have attached my extracted current working code in Pastebin. It has
> print statements and can be run in a new Maya session:
> https://pastebin.com/tN5bs6g0
>
> Any suggestions/recommendations are really appreciated. Please let me know
> if I wasn't clear enough.
> (I have a basic idea about metaclasses and class decorators, so any advice
> that includes those is welcome.)
>
> Thank you!
>
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