[PySide] sending data from urllib2.urlopen().read() via signal corrupts in receiver

Renaud Talon renaudtalon at fusefx.com
Sun Oct 22 20:54:37 CEST 2017

Hi Frank !

I first attempted to re-create your issue but I didn’t have any problem on my end. ( using PySide2 + Python3)

That said when I tried the same thing using Python2 I had the same issue as you did. I made a few changes and here is an example I created for you which works for both Python 2 and 3.


When using Python 3 “urllib.urlopen” returns a “bytes” object which PySide2 has no problem emitting and receiving as such: receivedData = Signal(bytes)

With Python 2 though using “urllib2.urlopen” I can print the image data within the thread and when checking the type it says “str” (which is fine since “str” and “bytes” are the same from what I understand in Py2)
That said after emitting the imgData as a string when I print the imgData type received from the signal it says “Unicode” instead of string and no matter what encoding I set it to (ascii, utf-8, utf-16) I can no longer read/print the imageData.
I am not sure why, this could be a Py2 + PySide2 bug or issue ?

To get around the issue I converted the data to a BytesIO object using the “io” module, setup the signal to use a “BytesIO” type instead of a “str” and that seems to work fine: receivedData = Signal(io.BytesIO)

I am not sure if this is the most elegant way. I’m curious to know what you guys think about this.

Take care,


Renaud Talon
Pipeline / TD

14823 Califa Street
Los Angeles, CA 91411
Office:   818-237-5052
Mobile:  310-430-8834

From: PySide [mailto:pyside-bounces+renaudtalon=fusefx.com at qt-project.org] On Behalf Of Frank Rueter | OHUfx
Sent: Sunday, October 22, 2017 2:20 AM
To: pyside at qt-project.org
Subject: Re: [PySide] sending data from urllib2.urlopen().read() via signal corrupts in receiver

quick follow up:
I am now writing the files to a temp directory and only passing the respective path via the signal, but I'm still curious how I would do this without writing anything to disk.

On 10/22/2017 09:18 PM, Frank Rueter | OHUfx wrote:

I am downloading a few images in a separate thread using QRunnable.
To download I am just using urllib2.urlopen() like this:

    def run(self):
        imageData = urllib2.urlopen(self.url).read()
        print 'emitted:', imageData
        self.signals.receivedData.emit(imageData) # this signal is declared like this: QtCore.Signal(str)

However, the receiving slot is receiving nothing:

    def setPixmap(self, imageData):
        print 'received:', imageData
        pixmap = QtGui.QPixmap()
        self.data['pixmap'] = pixmap

I guess this is too naive an approach to download image data in a separate thread?!

How can I fix this please?


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