[PyQt] How to add an argument to derived class's constructor

[Vincent Vande Vyvre]

Le 14/02/19 à 14:56, J Barchan a écrit :
>
>
> On Thu, 14 Feb 2019 at 13:34, J Barchan <jnbarchan at gmail.com 
> <mailto:jnbarchan at gmail.com>> wrote:
>
>     This may be as much a Python question as a PyQt one.  I come from
>     a C++ background.  I do not understand the syntax/code I need in a
>     class I am deriving from a PyQt class to allow a new parameter to
>     be passed to the constructor.
>
>     I see that I asked this question a long time ago at
>     https://stackoverflow.com/questions/45999732/python3-typing-overload-and-parameters
>     but never got an answer.
>
>     I now want to sub-class from QListWidgetItem. That starts with
>     these constructors:
>
>     QListWidgetItem(QListWidget *parent = nullptr, int type = Type)
>     QListWidgetItem(const QString &text, QListWidget *parent =
>     nullptr, int type = Type)
>     QListWidgetItem(const QIcon &icon, const QString &text,
>     QListWidget *parent = nullptr, int type = Type)
>     QListWidgetItem(const QListWidgetItem &other)
>
>     My sub-class should still support these constructors.  In addition
>     to the existing text, I want my sub-class to be able to store a
>     new optional value. At minimum/sufficient I want a new possible
>     constructor like one of the following:
>
>     MyListWidgetItem(const QString &text, const QVariant &value,
>     QListWidget *parent = nullptr, int type = Type)
>     # or
>     MyListWidgetItem(const QString &text, QVariant value = QVariant(),
>     QListWidget *parent = nullptr, int type = Type)
>
>     So for Python I know I start with a /typing overload/ definition
>     (for my editor) like
>
>     @typing.overload
>     def MyListWidgetItem(self, text: str, value: typing.Any, parent:
>     QListWidget=None, type: int=Type)
>     pass
>
>     Then I get to the /definition/ bit.  To cater for everything am I
>     supposed to do:
>
>     def __init__(self, *__args)
>     # Now what??
>     super().__init__(__args)
>
>     Is that how we do it?  Is it then my responsibility to look at
>     __args[1] to see if it's my value argument?  And remove it from
>     __args before passing it onto super().__init__(__args)?
>
>     Or, am I not supposed to deal with __args, and instead have some
>     definition with all possible parameters explicitly and deal with
>     them like that?
>
>     Or what? This is pretty fundamental to sub-classing to add
>     parameters where you don't own the code of what you're deriving
>     from.  It's easy in C-type languages; I'm finding it real to hard
>     to understand what I can/can't/am supposed to do for this, I'd be
>     really gratefully for a couple of lines to show me, please...! :)
>
>     -- 
>     Kindest,
>     Jonathan
>
>
> P.S.
> I think I got my overload a bit mixed up.  I meant I (think I) will have:
>
> class MyListWidgetItem(QListWidgetItem)
> @typing.overload
>     def __init__(self, text: str, value: typing.Any, parent: 
> QListWidget=None, type: int=Type)
> pass
>
>     def __init__(self, *__args)
> # Now what??
> super().__init__(__args)
>
>
> -- 
> Kindest,
> Jonathan
>
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Hi,

I use just that:

class ListItem(QListWidgetItem):
     def __init__(self, img, text, parent=None):
         super().__init__(parent)
         icon = QIcon()
         icon.addPixmap(QPixmap(img), QIcon.Normal, QIcon.Off)
         self.setIcon(icon)
         self.setText(text)

The arguments are examples, not mandatory.

Vincent

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