Python 3 wonders - Barry BDFL
While writing Nuitka I get to see an absurd
amount of CPython code. For a while now, it’s also CPython3.2 that I
look at. Checking out __future__ handling, I was surprised the other
day though, this really works:
# Python 3.2.3 (default, Jun 25 2012, 23:10:56)
# [GCC 4.7.1] on linux2
>>> from __future__ import barry_as_FLUFL
>>> 1 <> 2
True
>>> 1 != 2
File "<stdin>", line 1
1 != 2
^
SyntaxError: invalid syntax
It’s new in CPython3, and this the code that makes it possible, from the Python parser:
if (type == NOTEQUAL) {
if (!(ps->p_flags & CO_FUTURE_BARRY_AS_BDFL) &&
strcmp(str, "!=")) {
PyObject_FREE(str);
err_ret->error = E_SYNTAX;
break;
}
else if ((ps->p_flags & CO_FUTURE_BARRY_AS_BDFL) &&
strcmp(str, "<>")) {
PyObject_FREE(str);
err_ret->text = "with Barry as BDFL, use '<>' "
"instead of '!='";
err_ret->error = E_SYNTAX;
break;
}
}
Now who would think bad of that, would you? The fun aspect is, that Nuitka will easily supports it. By re-using the Python parser, it works out of the box, I only needed to add the flag value.
For fun, I tried to add a test that confirms - and then notice:
It doesn’t really work for CPython3.2 already.
The flag is only used for
evalandexecand not on the same level, so it’s only inherited.And “2to3” kindly removes that flag silently. It probably should raise an error.
So yeah, oddities in Python3!