On 12.05.2013, 22:19:55 David Cortesi wrote:
> For an app to be built with PyQt5/Qt5, I will have a
> QPlainTextEdit in which the document may be quite
> sizable, 500K characters or more.
> I will want at times to inspect the document character
> by character, or possibly apply Python relib REs to it.
> I am somewhat at sea regarding the relationship between
> a const QString such as returned by QPlainTextEdit.toPlainText()
> and a Python3 unicode string, and -- just in general -- about
> the best way to do intensive examination of big strings.
> Is there a copy involved in, e.g.
> docstring = unicode( myEditor.toPlainText() )
> I note that the PyQt4 QString reference omits the
> QString.begin() or .constBegin() etc methods that return an
> "STL-style iterator" so that's out. Is there some internal magic
> to integrate the QString type into Python's "for" mechanism
> so that "for c in myEditor.toPlainText()" might be more
> efficient than making a Python3 string and iterating on it?
> Also in regard to making intensive loops faster,
> how well do PyQtx calls integrate with Cython or PyPy?
> Thanks for any insights,
> Dave Cortesi
Hi,
This is how you cand find out things like this yourself:
"QPlainTextEdit.toPlainText()" is wrapped in
<python dir>\sip\PyQt5\QtWidgets\qplaintextedit.sip as
QString toPlainText() const;
QString is not wrapped normally as class, but defined as a mapped
type in <python dir>\sip\PyQt5\QtCore\qstring.sip.
The part interesting you is the conversion C++ -> Python:
%ConvertFromTypeCode
return qpycore_PyObject_FromQString(*sipCpp);
%End
This function can be found in the source code of PyQt5:
// Convert a QString to a Python Unicode object.
PyObject *qpycore_PyObject_FromQString(const QString &qstr)
{
PyObject *obj;
#if defined(PYQT_PEP_393)
obj = PyUnicode_FromKindAndData(PyUnicode_2BYTE_KIND, qstr.constData(),
qstr.length());
#elif defined(Py_UNICODE_WIDE)
QVector<uint> ucs4 = qstr.toUcs4();
if ((obj = PyUnicode_FromUnicode(NULL, ucs4.size())) == NULL)
return NULL;
memcpy(PyUnicode_AS_UNICODE(obj), ucs4.constData(),
ucs4.size() * sizeof (Py_UNICODE));
#else
if ((obj = PyUnicode_FromUnicode(NULL, qstr.length())) == NULL)
return NULL;
memcpy(PyUnicode_AS_UNICODE(obj), qstr.utf16(),
qstr.length() * sizeof (Py_UNICODE));
#endif
return obj;
}
As you can see, this will use a lot of memory in your case.
Best Regards,
Mathias Born
_______________________________________________
PyQt mailing list PyQt@riverbankcomputing.com
http://www.riverbankcomputing.com/mailman/listinfo/pyqt
