[PyQt] Writing dual python2/python3 code and the use of PyQt5.uic

Eli Schwartz eschwartz at archlinux.org
Sun Mar 24 01:48:30 GMT 2019

I've been devoting some time recently to incrementally porting a PyQt5
application "calibre" (https://github.com/kovidgoyal/calibre/) from
python2 to polyglot code, hoping to get it running with python3 at some
point. One recent stumbling block I hit was that it uses the uic module
to compile forms into a cStringIO.StringIO.

What I wanted to do was switch it to using the modern io interface, but
as it turns out, PyQt5 uses unqualified "str" instances to write out the
form. As a result, I cannot use io.StringIO on python2, and I cannot use
io.BytesIO on python3.

The uic module quite specifically seems to expect that it will
manipulate unicode strings. I was able to get io.StringIO buffers to
work correctly with both python2 and python3 after I modified two files
to contain a "from __future__ import unicode_literals":


Can this be added to at least these two files in the official
distribution? It seems to be a mistake that it ever assumed the str type.

Eli Schwartz
Arch Linux Bug Wrangler and Trusted User

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