[PyQt] QString and unicode problems

[Andrei Kopats]

Hi

I am developing PyQt app now, and I very often have crashes, connected with
QString usage. There are 2 reasons for exceptions:
- QString contains unicode characters
- python method called for Qt string. Sometimes called somewhere deep in
3rdparty code, such as os.path.blabla(QString))
See code examples at the end

It is easy to forget about QString conversions, because there are a few
different cases:
- if you define string in Python code - it is Python string
- if you take it from PyQt4 - it is QString
- If you passed Python string through signal-slot - it becomes QString.

The majority of methods may be called with either Python and Qt strings and
work fine.
Some bugs are not reproduced, while you use ascii, but, are reproduced, when
your user uses unicode
Too difficult, too lot of problems

QString problem wad discussed there:
http://thread.gmane.org/gmane.comp.python.pyqt-pykde/4037/
Now, when PyQt4 is widely used, it maybe to late to drop QString, because
some people use QString::endsWith(), and, probably, other compatibility
problem way happen.

But, maybe it is possible to renew this discussion and create something like
hybrid object, which is Python unicode string, but, has endsWith method (and
others, if there are API differences), so may pretend to be a QString



Code examples:
Problem 1:
In [1]: from PyQt4.QtCore import QString
In [2]: print QString('hello')
hello
In [3]: print QString('привет')  # Cyrillic symbols here
---
UnicodeEncodeErrorTraceback (most recent call last)
/home/a/code/mbox/core/src/lin/libonvif/ipython console in module()
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-11:
ordinal not in range(128)
Problem 2:
In [1]: from PyQt4.QtGui import QApplication, QFileDialog
In [2]: a = QApplication([])
In [3]: path = QFileDialog.getOpenFileName()
In [4]: path
Out[4]:
PyQt4.QtCore.QString(u'/home/a/code/mbox/core/src/lin/libonvif/Makefile')
In [5]: import os.path
In [6]: os.path.basename(path)
---
AttributeErrorTraceback (most recent call last)
/home/a/code/mbox/core/src/lin/libonvif/ipython console in module()
/usr/lib/python2.7/posixpath.pyc in basename(p)
110 def basename(p):
111 Returns the final component of a pathname
-- 112 i = p.rfind('/') + 1
113 return p[i:]
114
AttributeError: 'QString' object has no attribute 'rfind'

Best Regards,
Andrei Kopats,
https://github.com/hlamer/mksv3
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Re: [PyQt] QString and unicode problems

[Hans-Peter Jansen]

Am Tuesday 18 October 2011 11:07:24 schrieb Andrei Kopats:
 Hi

 I am developing PyQt app now, and I very often have crashes,
 connected with QString usage. There are 2 reasons for exceptions:
 - QString contains unicode characters

never had problems with that, as long as you provide proper unicode 
objects, or convert back to unicode objects.

 - python method called for Qt string. Sometimes called somewhere deep
 in 3rdparty code, such as os.path.blabla(QString))

return -ERRORBETWEENCHAIRANDKEYBOARD

 See code examples at the end

 It is easy to forget about QString conversions, because there are a
 few different cases:
 - if you define string in Python code - it is Python string
 - if you take it from PyQt4 - it is QString
 - If you passed Python string through signal-slot - it becomes
 QString.

- use V2 sip API and eliminate QStrings completely

http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/incompatible_apis.html

Please check, how things work for you using this, and call back.

Pete
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