[PyQt] Missing QIODevice::read overloads

Phil Thompson phil at riverbankcomputing.com
Sun May 31 16:18:30 BST 2015

On 25/05/2015 9:40 pm, Florian Bruhin wrote:
> Hi,
> I noticed the following QIODevice overloads are missing in PyQt:
>     qint64 QIODevice::read(char * data, qint64 maxSize)
>     qint64 QIODevice::readLine(char * data, qint64 maxSize)
> only the following are available:
>     QByteArray QIODevice::read(qint64 maxSize)
>     QByteArray QIODevice::readLine(qint64 maxSize = 0)
> The issue with those is that it's impossible to check for errors:
>     This function has no way of reporting errors; returning an empty
>     QByteArray can mean either that no data was currently available
>     for reading, or that an error occurred.
> The best workaround I found so far is to check if
> QIODevice::errorString is "Unknown error", but that's a hack...
> Maybe PyQt should provide the two other forms as well, when passing a
> mutable byte object (QByteArray/bytearray?) as first parameter?

I'm not sure what the best solution is. The reason the overloads are 
missing is that, following the normal PyQt conventions, they would 
return a str (Py2) or a bytes (Py3) but the signature would then be 
indistinguishable from the overloads that return a QByteArray. Possible 

1. Give the overloads a different Python name.

2. Change the existing methods to raise an exception (maybe initially a 
warning) on error.

3. Pass a mutable object as an argument. If all Python versions are 
still to be supported (something I don't think matters for PyQt5) then 
it would have to by a QByteArray, otherwise (if only Python v2.6 and 
later is to be supported) then a bytearray would do.

Given my previously stated desire to make better use of Python 
deprecation warnings and to correct old, bad design decisions, then I'm 
inclined towards option 2.


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