Surprising difference between StringIO.StringIO and io.StringIO

[Göktuğ Kayaalp]

io.StringIO only accepts Unicode input (i.e. u"multibyte string"),
while StringIO.StringIO accepts either 8 bit input or unicode input.
As you can see in the following excerpt from your traceback, the
'print_list' function creates an 8-bit string, which is then
(probably) passed to 'file.write' as the str variable, which actually
expects a unicode string, resulting in a TypeError:

File "/home/skipm/x86_64-linux3.1/lib/python2.7/traceback.py", line
23, in print_list
    '  File "%s", line %d, in %s' % (filename,lineno,name))
File "/home/skipm/x86_64-linux3.1/lib/python2.7/traceback.py", line
13, in _print
    file.write(str+terminator)

Python 2.x strings default to 8 bit. This is fixed (!) in Python 3.
I'd suggest switching to Python 3 if there is no reason to use 2.x. I
found this [*] little PDF back when I switched from 2 to 3, which was
helpful.

[*] http://ptgmedia.pearsoncmg.com/imprint_downloads/informit/promotions/python/python2python3.pdf

Greetings,

        Göktuğ.

On Thu, May 30, 2013 at 11:46 PM, Skip Montanaro <skip at pobox.com> wrote:
> Consider this quick session (Python 2.7 using the tip of the 2.7
> branch in Mercurial):
>
> % python2.7
> Python 2.7.5+ (2.7:93eb15779050, May 30 2013, 15:27:39)
> [GCC 4.4.6 [TWW]] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>>>> import traceback
>>>>
>>>> import StringIO
>>>> s1 = StringIO.StringIO()
>>>> traceback.print_stack(file=s1)
>>>> print s1.getvalue()
>   File "<stdin>", line 1, in <module>
>
>>>>
>>>> import io
>>>> s2 = io.StringIO()
>>>> traceback.print_stack(file=s2)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "/home/skipm/x86_64-linux3.1/lib/python2.7/traceback.py", line
> 269, in print_stack
>     print_list(extract_stack(f, limit), file)
>   File "/home/skipm/x86_64-linux3.1/lib/python2.7/traceback.py", line
> 23, in print_list
>     '  File "%s", line %d, in %s' % (filename,lineno,name))
>   File "/home/skipm/x86_64-linux3.1/lib/python2.7/traceback.py", line
> 13, in _print
>     file.write(str+terminator)
> TypeError: unicode argument expected, got 'str'
>>>> print s2.getvalue()
>
> What is it about io.StringIO that it doesn't like strings and requires
> Unicode?  This is on an OpenSUSE 12.1 system.  I have tried with LANG
> set to the default ("en_US.UTF-8") and to "C".  I also tried on a
> Solaris system with an older micro revision of Python 2.7.  Same
> result.
>
> Am I missing something about how io.StringIO works?  I thought it was
> a more-or-less drop-in replacement for StringIO.StringIO.
>
> Thx,
>
> Skip
> --
> http://mail.python.org/mailman/listinfo/python-list