<div dir="ltr"><div dir="ltr"><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 14 Feb 2019 at 13:34, J Barchan <<a href="mailto:jnbarchan@gmail.com">jnbarchan@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div style="font-family:tahoma,sans-serif">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.</div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif">I see that I asked this question a long time ago at <a href="https://stackoverflow.com/questions/45999732/python3-typing-overload-and-parameters" target="_blank">https://stackoverflow.com/questions/45999732/python3-typing-overload-and-parameters</a> but never got an answer.</div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif">I now want to sub-class from <span style="font-family:monospace,monospace">QListWidgetItem</span>. That starts with these constructors:</div><div style="font-family:tahoma,sans-serif"><br></div><div><span style="font-family:monospace,monospace">QListWidgetItem(QListWidget *parent = nullptr, int type = Type)<br>QListWidgetItem(const QString &text, QListWidget *parent = nullptr, int type = Type)<br>QListWidgetItem(const QIcon &icon, const QString &text, QListWidget *parent = nullptr, int type = Type)<br>QListWidgetItem(const QListWidgetItem &other)</span></div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif">My sub-class should still support these constructors. In addition to the existing <span style="font-family:monospace,monospace">text</span>, I want my sub-class to be able to store a new optional <span style="font-family:monospace,monospace">value</span>. At minimum/sufficient I want a new possible constructor like one of the following:</div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif"><span style="font-family:monospace,monospace">MyListWidgetItem(<span style="font-family:monospace,monospace">const QString &text, <span style="font-family:monospace,monospace"><span style="color:rgb(255,0,255)">const QVariant &value,</span> </span></span>QListWidget *parent = nullptr, int type = Type)</span></div><div style="font-family:tahoma,sans-serif"><span style="font-family:monospace,monospace"># or<br></span></div><div style="font-family:tahoma,sans-serif"><div style="font-family:tahoma,sans-serif"><span style="font-family:monospace,monospace">MyListWidgetItem(<span style="font-family:monospace,monospace">const QString &text, <span style="font-family:monospace,monospace"><span style="color:rgb(255,0,255)">QVariant value = QVariant(),</span> </span></span>QListWidget *parent = nullptr, int type = Type)</span></div><div style="font-family:tahoma,sans-serif"><br></div></div><div style="font-family:tahoma,sans-serif">So for Python I know I start with a <i>typing overload</i> definition (for my editor) like <br></div><div style="font-family:tahoma,sans-serif"><br></div><div><span style="font-family:monospace,monospace">@typing.overload</span></div><div><span style="font-family:monospace,monospace">def MyListWidgetItem(self, text: str, value: typing.Any, parent: QListWidget=None, type: int=Type)</span></div><div><span style="font-family:monospace,monospace"> pass<br></span></div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif">Then I get to the <i>definition</i> bit. To cater for everything am I supposed to do:</div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif"><div><span style="font-family:monospace,monospace"><span class="gmail_default" style="font-family:tahoma,sans-serif"></span>def __init__(self, *__args)</span></div><div><span style="font-family:monospace,monospace"> # Now what??<br></span></div><div><span style="font-family:monospace,monospace"> super().__init__(__args)<br></span></div></div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif"></div><div style="font-family:tahoma,sans-serif">Is that how we do it? Is it then my responsibility to look at <span style="font-family:monospace,monospace">__args[1]</span> to see if it's my <span style="font-family:monospace,monospace">value</span> argument? And remove it from <span style="font-family:monospace,monospace">__args</span> before passing it onto <span style="font-family:monospace,monospace">super().__init__(__args)</span>?<br></div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif">Or, am I not supposed to deal with <span style="font-family:monospace,monospace">__args</span>, and instead have some definition with all possible parameters explicitly and deal with them like that?</div><div style="font-family:tahoma,sans-serif"><br></div><div style="font-family:tahoma,sans-serif">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...! :)<br clear="all"></div><br>-- <br><div dir="ltr" class="gmail-m_-6986055192168723530gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><span style="font-family:tahoma,sans-serif">Kindest,</span></div><div><span style="font-family:tahoma,sans-serif">Jonathan</span></div></div></div></div></div></div></div></div></div>
</blockquote></div><br clear="all"><div style="font-family:tahoma,sans-serif" class="gmail_default">P.S.</div><div style="font-family:tahoma,sans-serif" class="gmail_default">I think I got my overload a bit mixed up. I meant I (think I) will have:</div><div style="font-family:tahoma,sans-serif" class="gmail_default"><br></div><div style="font-family:tahoma,sans-serif" class="gmail_default"><span style="font-family:monospace,monospace">class MyListWidgetItem(QListWidgetItem)</span><span style="font-family:monospace,monospace"><span class="gmail_default" style="font-family:tahoma,sans-serif"><br></span></span></div><div style="font-family:tahoma,sans-serif" class="gmail_default"><span style="font-family:monospace,monospace"><span class="gmail_default" style="font-family:tahoma,sans-serif"></span></span><div><div style="font-family:tahoma,sans-serif"><div><div><span style="font-family:monospace,monospace"> @typing.overload</span></div><div><span style="font-family:monospace,monospace"><span style="font-family:monospace,monospace"> def __init__(<span style="font-family:monospace,monospace">self, text: str, value: typing.Any, parent: QListWidget=None, type: int=Type)</span></span></span><div><span style="font-family:monospace,monospace"> pass</span></div><div><span style="font-family:monospace,monospace"><br></span></div><span style="font-family:monospace,monospace"> def __init__(self, *__args)</span></div></div><div><span style="font-family:monospace,monospace"> # Now what??<br></span></div><div><span style="font-family:monospace,monospace"> super().__init__(__args)<br></span></div></div><div style="font-family:tahoma,sans-serif"><br></div><span style="font-family:monospace,monospace"></span></div></div><br>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><span style="font-family:tahoma,sans-serif">Kindest,</span></div><div><span style="font-family:tahoma,sans-serif">Jonathan</span></div></div></div></div></div></div>