(curses) addstr() takes str in Python 3

[Trundle]

BPO	6745
Nosy	@vstinner, @Trundle, @ambv, @akheron
Files	umlaut2x.py: Umlauts working in Python 2.x umlaut3x.py: Umlauts not working in Python 3.x curses_charset.patch getkey_sample.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/ambv'
closed_at = <Date 2012-06-04.23:37:38.789>
created_at = <Date 2009-08-20.21:54:52.568>
labels = ['type-bug', 'library']
title = '(curses) addstr() takes str in Python 3'
updated_at = <Date 2012-06-04.23:37:38.769>
user = 'https://github.com/Trundle'

bugs.python.org fields:

activity = <Date 2012-06-04.23:37:38.769>
actor = 'vstinner'
assignee = 'lukasz.langa'
closed = True
closed_date = <Date 2012-06-04.23:37:38.789>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2009-08-20.21:54:52.568>
creator = 'Trundle'
dependencies = []
files = ['14750', '14751', '14792', '19623']
hgrepos = []
issue_num = 6745
keywords = ['patch']
message_count = 11.0
messages = ['91786', '92019', '92020', '92021', '92023', '92024', '92025', '121318', '121346', '140380', '162307']
nosy_count = 4.0
nosy_names = ['vstinner', 'Trundle', 'lukasz.langa', 'petri.lehtinen']
pr_nums = []
priority = 'high'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue6745'
versions = ['Python 3.2']

[Trundle]

In Python 3, curses requires a str for addstr() where I think it should
take bytes instead. Otherwise it is impossible to output anything other
than ASCII (which is even more or less stated on top of curses'
documentation).

See the attached script "umlaut2x.py" for Python 2.6: Outputting
umlauts works fine, both in single-byte and multi-byte environments.

The attached script "umlaut3x.py" is the same script translated to
Python 3. Note that the output here always seems to be utf-8, which is
plain wrong.

A quick test where I changed addstr() to take bytes instead of str
confirmed that outputting other characters than ASCII would work then
in Python 3, too. There are perhaps more places where the types are
wrong. If someone confirms this issue and it is desired, I could
provide a patch.

[vstinner]

First, make sure that your Python3 build uses libncursesw and not
libncurses, because libncursesw supports unicode, whereas libncurses
doesn't... On UNIX, use the following command to check this:

ldd $(./python -c "import _curses; print(curses.__file_)")|grep curses

Note that the output here always seems to be utf-8,
which is plain wrong.

Yes, addstr() always uses utf8 to convert unicode to bytes. It's wrong
if the terminal uses a different charset. But I'm not sure that using
bytes is a better idea: since you would like to print characters,
unicode is the right type.

An idea would be to use a configurable charset. Eg. add a 'charset'
attribute to a window (or to the module).

[vstinner]

See also issue bpo-4787

[Trundle]

Yes, it uses a version of ncurses which supports wide characters, I
checked that.

I agree that using bytes instead may not be the preferred solution in
Python 3. The point is, currently, it is broken if the user does not
use an utf-8 environment.

[vstinner]

I don't really understand because your example, umlaut3x.py, works
correctly on my computer (py3k, ubunty jaunty).

The point is, currently, it is broken if the user
does not use an utf-8 environment.

So the problem is that the charset is hardcoded to utf8. You would like
to be able to change that. Or better, than Python guess your terminal
charset. Right?

[Trundle]

Of course it works for you. As you stated in issue bpo-4787, your locale
is 'fr_FR.UTF-8'.

And I don't want Python to guess my terminal's encoding. I want Python
to respect my locale. Which is 'de_DE@euro', and not utf-8.

[vstinner]

Here is a first patch to add a method setcharset() to the window class.

Using my patch, you can fix your example by adding the line:

   screen.setcharset(<your charset>)

before addstr().

It's an initial hack to fix the issue. Next steps are:

• use something better than utf8 as the default charset, maybe
  locale.getpreferredencoding()
• copy the charset on new window creation?

[ambv]

We'll try to solve this for 3.2.

[Trundle]

Note that getkey() is broken, too. I attached a simple script to demonstrate that. If you run it and enter some non-ascii input, you can see that getkey() returns an utf-8 encoded str (in my utf-8 environment at least, I haven't check if it's always utf-8 or if it depends on the locale).

[vstinner]

I created issue bpo-12567 to fix the Unicode support of the curses module in Python 3.

[vstinner]

The issue bpo-12567 fixed this one:

• umlaut3x.py now works in Python 3.3 with an encoding different than UTF-8: Python automatically detects (and uses) the locale encoding
• getkey_sample.py can be patched to handle Unicode correctly using get_wch() instead of getkey()