Format strings not marked correctly

[youtux]

This is a problem affecting the extraction of string from python files.

While format strings like "Hello %(name)s" are correctly extracted and marked with the #, python-format marker, strings like "Hello {name}" are not marked, and translators may not realize that and change the formatting part, resulting in KeyErrors when actually evaluating the string. xgettext will mark them correctly, with the #, python-brace-format marker.

How to reproduce

# asd.py
_("old style hello %(name)s")

_("new style hello {name}")

Run pybabel extraction:

$ pybabel extract asd.py -o asd.babel.po
extracting messages from asd.py
writing PO template file to asd.po

The asd.babel.po contains these entries:

...
#: asd.py:1
#, python-format
msgid "old style hello %(name)s"
msgstr ""

#: asd.py:3
msgid "new style hello {name}"
msgstr ""

The last entry is not marked as a format string.

Run the following command to check what instead xgettext does:

$ xgettext -L Python --keyword=_ asd.py -o - > asd.xgettext.po

The asd.xgettext.po contains these entries:

#: asd.py:1
#, python-format
msgid "old style hello %(name)s"
msgstr ""

#: asd.py:3
#, python-brace-format
msgid "new style hello {name}"
msgstr ""

Note that the last string is marked as #, python-brace-format.

Use case

I have this problem when automatically translating using podebug to generate catchy unicode strings for development purposes. The tool will not see that "hello {name}" is a format string, and it will translate it to "ħḗŀŀǿ {ƞȧḿḗ}", causing a KeyError when calling _("hello {name}").format(name="Alessio"). This can be a problem when using tools like Transifex that protect you from touching part of the string that you shouldn't. If they are not marked correctly, the tool can't do much.

[ronanpaixao]

Also, even if marking the .po file manually, pybabel compile doesn't handle the #, python-brace-format properly:

(...)
#: somefile.py:1363
#, python-brace-format
msgid "Percentil 95% da Validação 1: {}"
msgstr "95% percentile of Validation 1: {}"

pybabel compile -d . -i translations.po -l en -f --statistics

122 of 122 messages (100%) translated in translations.po
error: translations.po:518: placeholders are incompatible
compiling catalog translations.po to .\en\LC_MESSAGES\translations.mo
1 errors encountered.

Using Anaconda3 64-bit, Python 3.8.13, babel 2.10.1, Windows 10.

While pybabel indicates the error, it also says that all messages were translated. Gotta test it properly though.