[PyQt] Slot type validation: int/qint64

[Phil Thompson]

On 29 Apr 2016, at 7:36 pm, Florian Bruhin <me at the-compiler.org> wrote:
> 
> * Florian Bruhin <me at the-compiler.org> [2016-04-26 20:11:49 +0200]:
>> Hi!
>> 
>> Thanks to the slot type validation of PyQt 5.6 I discovered a lot of cases
>> where my decorations where plain wrong...
>> 
>> However in this case I'm unsure what's going on:
>> 
>> 	Traceback (most recent call last):
>> 	  File ".../qutebrowser/browser/webpage.py", line 327, in on_unsupported_content
>> 		suggested_filename=suggested_filename)
>> 	  File ".../qutebrowser/browser/downloads.py", line 884, in fetch
>> 		download = DownloadItem(reply, self._win_id, self)
>> 	  File ".../qutebrowser/browser/downloads.py", line 332, in __init__
>> 		self.init_reply(reply)
>> 	  File ".../qutebrowser/browser/downloads.py", line 430, in init_reply
>> 		reply.downloadProgress.connect(self.stats.on_download_progress)
>> 	TypeError: decorated slot has no signature compatible with downloadProgress(qint64,qint64)
>> 
>> [...]
>> 
>> Using 'qint64', 'qint64' instead works.
>> 
>> I've tried to create a minimal example:
>> 
>> [...]
>> 
>> But that seems to work fine for some reason...
> 
> I can reproduce the issue with the attached example (thanks to ntome
> in the #pyqt IRC channel).

The problem is that a Python int is mapped to a C++ int in the slot signature, even though a Python int is capable of storing much bigger values. Connecting a qint64 to a C++ int is invalid, hence the error.

A fix for this would be map a Python int to the biggest C++ integer type. However I am uncomfortable making such a change without a lot more thought and experimentation (particularly when handling quint64).

In the meantime the workaround (which should always work) is to use 'qint64' as you are doing.

Phil