[kmike84]

In case of NLTK unicode_literals ("unicode by default") fixed a lot of bugs and made other bugs visible, so mileage may vary :)

Could you give an example of cases where unicode_literals is a terrible idea?

3.2 is important for newcomer experience IMHO; it is very common for people starting with Python to use 3.x version and wonder why the code doesn't work. It's a pity high-profile packages are dropping 3.2 support, I wasn't aware Requests and Jinja2 dropped it.

utf8 __str__ definitely caused issues for Django (e.g. `print mymodel` sometimes fails in REPL in Windows with Russian locale); people using REPL in Windows are too used to such errors so they don't complain and blame Windows for this, but that doesn't mean there is no issue.

[the_mitsuhiko]

So will latin1 `__str__` on Russian locales. So will ASCII `__str__` on any locale that is not ASCII compatible. You can't expect the impossible.

In regards to cases where unicode_literals is a terrible idea is any piece of code that then suddenly gets a unicode string which does not expect it. Because unicode coercion in 2.x spreads like a cancer you might not see the failure until someone uses your API. I still have to fix bugs where people accidentally send things coerced to unicode to an API that does not support it.

Additionally: newcomers still should not be using Python 3. There are just too many remaining issues that are annoying to deal with.

[kmike84]

Are there non-ascii compatible encodings that are default in any OSes? With ascii-incompatible system/terminal encoding a lot of software will stop working. Strange things happen, but this looks like a theoretical issue, and ascii looks safe. In Python 2.x __str__ of all standard container types are ASCII-only (even if elements has non-ascii __str__), and __repr__ of standard objects is also ASCII-only as far as I can tell. ASCII-only is an option, and it is not uncommon and relatively safe (but it has its own issues of course).

It was exactly this unicode_literals property (turning everything into unicode) that helped to reveal bugs :) For example, models were trained on bytestrings under Python 2.x, and nobody remembers what was the encoding of the text models were trained on. This was unnoticed for several years because instead of raising an exception functions just handled some egde cases (e.g. unicode punctuation) in a suboptimal way. This leads to almost correct results, but with less accuracy/precision/recall. After changing to "unicode everywhere" the issue became visible.

The issue was not with cancer-like turning text into unicode, issue was with the code that works with text and doesn't support unicode. Python 2.x standard library has such APIs, and this causes troubles, but I don't see how it is a bug in the code that works with text and returns unicode.

What I'm writing are common words and a standard "unicode mantra", but anyways.

We could say "programmers should just handle encodings properly, and unicode_literals have nothing to do with this", but this doesn't always work. "Unicode everywhere" makes some code changes necessary, but some of these changes reveal real bugs.

Another story: I took 2 different courses from 2 different top-notch universities at coursera.org where instructors gave us starter code (written in Python 2.x) for programming assignments. The code was not bad, but there were many cases of incorrect encodings handling in most of the provided files (such errors that would be impossible in Python 3.x) - this was the code that was supposed to teach students something (including Python programming).

What I like about unicode_literals is that it makes things more consistent and easier (at least for me) to reason about: if variable is unicode under 3.x, it is unicode in 2.x, the same applies to bytestrings. In cases where different behaviour is necessary (e.g. because of non-unicode API in 2.x stdlib), explicit str("foo") is used; otherwise code is written in Python 3.x and works with the same semantics under Python 2.x.

Just curious, what newcomer issues are you talking about, and who do you mean by "newcomers"?