typo... meant of course foo(*([0]*300)) Andrea
On Mon, Aug 6, 2018 at 9:57 AM Andrea Griffini <agr...@tin.it> wrote: > With Python 2.7.15 what fails is a call with explicit arguments (e.g. > `foo(0,0,0 ... 0,0)`), not the function definition. > Calling with `foo([0]*300)` instead works. > > > On Mon, Aug 6, 2018 at 7:18 AM Stephen McDowell <sjm...@cornell.edu> > wrote: > >> Hello Python Gurus, >> >> TL;DR: 3.7 released functions having greater than 255 arguments. Despite >> explicit checks for this in 2.x, no such limit is actually imposed -- why? >> >> In the 3.7 release notes "Other Language Changes" section ( >> https://docs.python.org/3.7/whatsnew/3.7.html#other-language-changes), >> the first bullet point denotes >> >> > More than 255 arguments can now be passed to a function, and a function >> can now have more than 255 parameters. (Contributed by Serhiy Storchaka in >> bpo-12844 <https://bugs.python.org/issue12844> and bpo-18896 >> <https://bugs.python.org/issue18896>.) >> >> Now lets get something straight: unless I want to exclusively support >> Python 3.7 or higher, I must make sure I obey the <255 rule. Use *args // >> **kwargs, etc. I'm totally ok with that, 2020 is already here in my mind ;) >> >> Curiosity is the reason I'm reaching out. Upon further investigation and >> some discussion with like-minded Python enthusiasts, the code being patched >> by Serhiy Storchaka is present in e.g., Python 2.7 ( >> https://github.com/python/cpython/blob/2.7/Python/ast.c#L2013-L2016) >> >> if (nargs + nkeywords + ngens > 255) { >> ast_error(n, "more than 255 arguments"); >> return NULL; >> } >> >> Despite that code, as demonstrated with the supplemental output in the >> post script, *no 2.x versions fail with >255 arguments*. In contrast, >> 3.x where x<7 all do fail (as expected) with a SyntaxError. To test >> this, I tried every minor release of python (excluding v1, arbitrarily >> choosing the latest patch release of a minor version) with the following >> snippet via the -c flag >> >> /path/to/pythonX.Y -c 'exec("def foo(" + ", ".join(["a" + str(i) for >> i in range(1, 300)]) + "): pass")' >> >> Which tries to construct a function >> >> def foo(a0, a1, ..., a299): pass >> >> I've looked at the C code for a while and it is entirely non-obvious what >> would lead to python *2* *allowing* >255 arguments. Anybody happen to >> know how / why the python *2* versions *succeed*? >> >> Thank you for reading, this is not a problem, just a burning desire for >> closure (even if anecdotal) as to how this can be. I deeply love python, >> and am not complaining! I stumbled across this and found it truly >> confounding, and thought the gurus here may happen to recall what changed >> in 3.x that lead the the error condition actually being asserted :) >> >> Sincerely, >> >> Stephen McDowell >> >> P.S. On a Fedora 25 box using GCC 6.4.1, I lovingly scripted the >> installation of all the python versions just to see if it truly was a 2.x / >> 3.x divide. The results of running `python -V` followed by the `python >> -c 'exec("def foo...")'` described above, with some extra prints for >> clarity are as follows (script hackily thrown together in ~30minutes not >> included, so as not to make your eyes bleed): >> >> >> ******************************************************************************** >> Python 2.0.1 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 2.1.3 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 2.2.3 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 2.3.7 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 2.4.6 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 2.5.6 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 2.6.9 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 2.7.15 >> ==> Greater than 255 Arguments supported >> >> ******************************************************************************** >> Python 3.0.1 >> Traceback (most recent call last): >> File "<string>", line 1, in <module> >> File "<string>", line 1 >> SyntaxError: more than 255 arguments >> >> ******************************************************************************** >> Python 3.1.5 >> Traceback (most recent call last): >> File "<string>", line 1, in <module> >> File "<string>", line 1 >> SyntaxError: more than 255 arguments >> >> ******************************************************************************** >> Python 3.2.6 >> Traceback (most recent call last): >> File "<string>", line 1, in <module> >> File "<string>", line 1 >> SyntaxError: more than 255 arguments >> >> ******************************************************************************** >> Python 3.3.7 >> Traceback (most recent call last): >> File "<string>", line 1, in <module> >> File "<string>", line 1 >> SyntaxError: more than 255 arguments >> >> ******************************************************************************** >> Python 3.4.9 >> Traceback (most recent call last): >> File "<string>", line 1, in <module> >> File "<string>", line 1 >> SyntaxError: more than 255 arguments >> >> ******************************************************************************** >> Python 3.5.6 >> Traceback (most recent call last): >> File "<string>", line 1, in <module> >> File "<string>", line 1 >> SyntaxError: more than 255 arguments >> >> ******************************************************************************** >> Python 3.6.6 >> Traceback (most recent call last): >> File "<string>", line 1, in <module> >> File "<string>", line 1 >> SyntaxError: more than 255 arguments >> >> ******************************************************************************** >> Python 3.7.0 >> ==> Greater than 255 Arguments supported >> >> P.P.S. Seriously, I LOVE PYTHON <3 It was so easy to download, >> configure, build, and install each of these versions, and run the test! >> Thank you :) >> _______________________________________________ >> Python-Dev mailing list >> Python-Dev@python.org >> https://mail.python.org/mailman/listinfo/python-dev >> Unsubscribe: >> https://mail.python.org/mailman/options/python-dev/agriff%40tin.it >> >
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