Hi.Python 3.6.2 crashes when interpreting lines with the text "async \" (future keyword 'async' and ending with a backslash).Tested in a docker environment (debian jessie). (see github.com/0xquad/docker-python36 if needed)Examples:$ docker run -ti --rm python364c09392f83c8">root@4c09392f83c8:/# python3.6Python 3.6.2 (default, Aug  4 2017, 14:35:04)[GCC 6.4.0 20170724] on linuxType "help", "copyright", "credits" or "license" for more information.>>> async \...  File "<stdin>", line 1    \ufffd\ufffdF\ufffd\ufffd         ^SyntaxError: invalid syntax>>> async \Segmentation fault4c09392f83c8">root@4c09392f83c8:/#Also,----- file: test.py#/usr/bin/python3.6async \<repeated 30000 times>-----$ ./test.pySegmentation fault$Haven't taken the time to produce a backtrace or investigate with latest the dev versions or any further.Let me know if I can assist in any way.

This issue is fixed in the master branch (version 3.7.0 alpha 2). The issue was fixed in this PR:https://github.com/python/cpython/pull/1669The cause is that async was not a proper keyword and the parser segfaults when checking for the new token and parsing the newline. In particular, this happens here:translate_newlines atParser/tokenizer.c:713713         buf = PyMem_MALLOC(needed_length);This is the stack trace:#0  _PyObject_Alloc (ctx=<optimized out>, elsize=10, nelem=1, use_calloc=0) atObjects/obmalloc.c:806#1  _PyObject_Malloc (ctx=<optimized out>, nbytes=10) atObjects/obmalloc.c:985#2  0x0000000000453020 in translate_newlines (tok=0x9187b0, exec_input=0, s=0x7ffff7fa40e0 "async \\\n") atParser/tokenizer.c:713#3  tok_nextc (tok=tok@entry=0x9187b0) atParser/tokenizer.c:943#4  0x0000000000454948 in tok_get (tok=tok@entry=0x9187b0,p_start=p_start@entry=0x7fffffffdc40,p_end=p_end@entry=0x7fffffffdc50)    atParser/tokenizer.c:1382#5  0x0000000000455749 in PyTokenizer_Get (tok=tok@entry=0x9187b0,p_start=p_start@entry=0x7fffffffdc40,p_end=p_end@entry=0x7fffffffdc50)    atParser/tokenizer.c:1902#6  0x000000000045158d in parsetok (tok=0x9187b0, g=<optimized out>, start=256,err_ret=err_ret@entry=0x7fffffffdce0,flags=flags@entry=0x7fffffffdcd0) atParser/parsetok.c:208#7  0x0000000000452280 in PyParser_ParseFileObject (fp=<optimized out>,filename=filename@entry=0x7ffff7f1b848, enc=<optimized out>,    g=<optimized out>, start=<optimized out>, ps1=<optimized out>, ps2=0x7ffff7e63648 "... ",err_ret=err_ret@entry=0x7fffffffdce0,flags=flags@entry=0x7fffffffdcd0) atParser/parsetok.c:134#8  0x0000000000433949 in PyParser_ASTFromFileObject (fp=<optimized out>, filename=0x7ffff7f1b848, enc=<optimized out>,    start=<optimized out>, ps1=<optimized out>, ps2=<optimized out>, flags=0x7fffffffde90, errcode=0x7fffffffdd80, arena=0x7ffff7fe2168)    atPython/pythonrun.c:1166#9  0x0000000000433b5b in PyRun_InteractiveOneObject (fp=fp@entry=0x7ffff74b2640 <_IO_2_1_stdin_>,filename=filename@entry=0x7ffff7f1b848,flags=flags@entry=0x7fffffffde90) atPython/pythonrun.c:218#10 0x0000000000433eae in PyRun_InteractiveLoopFlags (fp=fp@entry=0x7ffff74b2640 <_IO_2_1_stdin_>,filename_str=filename_str@entry=0x5dd7a4 "<stdin>",flags=flags@entry=0x7fffffffde90) atPython/pythonrun.c:115#11 0x0000000000433fbc in PyRun_AnyFileExFlags (fp=0x7ffff74b2640 <_IO_2_1_stdin_>, filename=0x5dd7a4 "<stdin>", closeit=0,    flags=0x7fffffffde90) atPython/pythonrun.c:77#12 0x00000000004476fa in run_file (p_cf=0x7fffffffde90, filename=<optimized out>, fp=0x7ffff74b2640 <_IO_2_1_stdin_>) atModules/main.c:341#13 Py_Main (argc=argc@entry=1,argv=argv@entry=0x910010) atModules/main.c:895#14 0x000000000041e17a in main (argc=1, argv=<optimized out>) at ./Programs/python.c:102After applying commitac317700ce7439e38a8b420218d9a5035bba92ed the issue is fixed.Does it make sense to backportac317700ce7439e38a8b420218d9a5035bba92ed to 3.6?

> Does it make sense to backportac317700ce7439e38a8b420218d9a5035bba92ed to 3.6?No, async was not a keyword in Python 3.6 on purpose. Making it a keyword can break a lot of code.I confirm that Python 3.6 still crashs with a very high number of "async " prefixes: try attached async_parser_crash.py.Extract of the gdb traceback on a crash:(...)#665 0x0000000000454867 in tok_get (tok=0x7fffff8b98c0,     p_start=0x7fffff8b9cb8, p_end=0x7fffff8b9cb0) atParser/tokenizer.c:1571#666 0x0000000000454867 in tok_get (tok=0x7fffff8b9d40,     p_start=0x7fffff8ba138, p_end=0x7fffff8ba130) atParser/tokenizer.c:1571#667 0x0000000000454867 in tok_get (tok=0x7fffff8ba1c0,     p_start=0x7fffff8ba5b8, p_end=0x7fffff8ba5b0) atParser/tokenizer.c:1571#668 0x0000000000454867 in tok_get (tok=0x7fffff8ba640,     p_start=0x7fffff8baa38, p_end=0x7fffff8baa30) atParser/tokenizer.c:1571#669 0x0000000000454867 in tok_get (tok=0x7fffff8baac0,     p_start=0x7fffff8baeb8, p_end=0x7fffff8baeb0) atParser/tokenizer.c:1571#670 0x0000000000454867 in tok_get (tok=0x7fffff8baf40,     p_start=0x7fffff8bb338, p_end=0x7fffff8bb330) atParser/tokenizer.c:1571#671 0x0000000000454867 in tok_get (tok=0x7fffff8bb3c0,     p_start=0x7fffff8bb7b8, p_end=0x7fffff8bb7b0) atParser/tokenizer.c:1571(...)It looks like a stack overflow.The tokenizer may fail earlier on "async async ".

New changeset690c36f2f1085145d364a89bfed5944dd2470308 by Victor Stinner (Pablo Galindo) in branch '3.6':[3.6]bpo-31852: Fix segfault caused by using the async soft keyword (GH-4122)https://github.com/python/cpython/commit/690c36f2f1085145d364a89bfed5944dd2470308

Thank you Alexandre Hamelin for the bug report and Pablo Galindo for the fix ;-)

Awesome work, thanks to you!Would it also be the case for 'await' ?

> Would it also be the case for 'await' ?"async" requires to maintain a "async_def" state. It seems like await doesn't need a state for itself, but rely on the "async_def" state which has been fixed.Extract ofParser/tokenizer.c:            /* Current token length is 5. */            if (tok->async_def) {                /* We're inside an 'async def' function. */                if (memcmp(tok->start, "async", 5) == 0) {                    return ASYNC;                }                if (memcmp(tok->start, "await", 5) == 0) {                    return AWAIT;                }            }