[PyQt] PyQt documentation where PyQt function is not same as Qt C++ function

Hans-Peter Jansen hpj at urpla.net
Mon Nov 27 16:38:43 GMT 2017

On Montag, 27. November 2017 15:53:28 J Barchan wrote:
> ​​
> Dear PyQt developers/maintainers/documenters,
> [Also cc'ed to "Florian Bruhin", as I believe you have indicated that you
> are "The Man"!]
> I'm getting a little peeved by the problems which arise when you seem to
> have chosen to make a PyQt function differ somewhat (in return result, so
> far) from the corresponding Qt C++ function, but no documentation to
> explain can be found.  (This may apply only to PyQt5, not PyQt4, I don't
> know.)
> I was just trying to write an override in my own class for
> QRegularExpression.validate().  The Qt documentation (
> http://doc.qt.io/qt-5/qregularexpressionvalidator.html#validate) shows:
> QValidator::State <http://doc.qt.io/qt-5/qvalidator.html#State-enum>
> QRegularExpressionValidator::validate(QString
> <http://doc.qt.io/qt-5/qstring.html> &*input*, int &*pos*) const
> So I expect it to return a QValidator.State.  However, QtGui.pyi shows:
> def validate(self, input: str, pos: int) ->
> typing.Tuple[QValidator.State, str, int]: ...
> So this is a tuple, with an extra str & int returned.
> Apart from the fact that it's a tuple instead of a plain enum returned, I
> have *no idea* what the extra str & int might be, what to do with them, etc.

This is due to the poor C++ way of dealing with multiple return values, while avoiding to 
define yet another typedef... You supply references to parameter values by the ampersand 
(&). Expect these values modified in the method call. 

In Python, that concept translates to a tuple return value rather naturally. PyQt follows the 
pattern "return value", "1st reference value", "2nd..." for the returned tuple order.


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