this triggers an assertion when run with debug enabled:

$ gdb ./python 
GNU gdb (Ubuntu 8.1-0ubuntu3.2) 8.1.0.20180409-git
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Reading symbols from ./python...done.
warning: File "/home/asottile/workspace/cpython/python-gdb.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
To enable execution of this file add
	add-auto-load-safe-path /home/asottile/workspace/cpython/python-gdb.py
line to your configuration file "/home/asottile/.gdbinit".
To completely disable this security protection add
	set auto-load safe-path /
line to your configuration file "/home/asottile/.gdbinit".
For more information about this security protection see the
"Auto-loading safe path" section in the GDB manual.  E.g., run from the shell:
	info "(gdb)Auto-loading safe path"
(gdb) run t2.py
Starting program: /home/asottile/workspace/cpython/python t2.py
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
python: Python/compile.c:3545: compiler_nameop: Assertion `scope || PyUnicode_READ_CHAR(name, 0) == '_'' failed.

Program received signal SIGABRT, Aborted.
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
51	../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007ffff7060801 in __GI_abort () at abort.c:79
#2  0x00007ffff705039a in __assert_fail_base (
    fmt=0x7ffff71d77d8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", 
    assertion=assertion@entry=0x555555815190 "scope || PyUnicode_READ_CHAR(name, 0) == '_'", file=file@entry=0x555555814233 "Python/compile.c", 
    line=line@entry=3545, 
    function=function@entry=0x555555814180 <__PRETTY_FUNCTION__.17589> "compiler_nameop") at assert.c:92
#3  0x00007ffff7050412 in __GI___assert_fail (
    assertion=assertion@entry=0x555555815190 "scope || PyUnicode_READ_CHAR(name, 0) == '_'", file=file@entry=0x555555814233 "Python/compile.c", 
    line=line@entry=3545, 
    function=function@entry=0x555555814180 <__PRETTY_FUNCTION__.17589> "compiler_nameop") at assert.c:101
#4  0x000055555568e946 in compiler_nameop (c=0x7fffffffdb40, 
    name=<optimized out>, ctx=Load) at Python/compile.c:3545
#5  0x000055555569020e in compiler_visit_expr1 (c=c@entry=0x7fffffffdb40, 
    e=0x555555b739d0) at Python/compile.c:5027
#6  0x000055555569027f in compiler_visit_expr (c=0x7fffffffdb40, 
    e=<optimized out>) at Python/compile.c:5052
#7  0x0000555555693570 in compiler_visit_argannotation (
    c=c@entry=0x7fffffffdb40, id=0x7ffff7f95d60, annotation=<optimized out>, 
    names=names@entry=0x7ffff66217d0) at Python/compile.c:2045
#8  0x000055555569363e in compiler_visit_argannotations (
    c=c@entry=0x7fffffffdb40, args=0x555555b739c0, 
    names=names@entry=0x7ffff66217d0) at Python/compile.c:2066
#9  0x00005555556936b2 in compiler_visit_annotations (
    c=c@entry=0x7fffffffdb40, args=args@entry=0x555555b73a28, 
    returns=returns@entry=0x0) at Python/compile.c:2094
#10 0x00005555556939fc in compiler_function (c=0x7fffffffdb40, 
    s=0x555555b73ab8, is_async=is_async@entry=0) at Python/compile.c:2214
#11 0x0000555555693dad in compiler_visit_stmt (c=c@entry=0x7fffffffdb40, 
    s=0x555555b73ab8) at Python/compile.c:3332
---Type <return> to continue, or q <return> to quit---
#12 0x0000555555693b8f in compiler_function (c=0x7fffffffdb40, 
    s=<optimized out>, is_async=is_async@entry=0) at Python/compile.c:2238
#13 0x0000555555693dad in compiler_visit_stmt (c=c@entry=0x7fffffffdb40, 
    s=0x555555b73b00) at Python/compile.c:3332
#14 0x0000555555694022 in compiler_body (c=c@entry=0x7fffffffdb40, 
    stmts=0x555555b73960) at Python/compile.c:1816
#15 0x0000555555694754 in compiler_mod (c=c@entry=0x7fffffffdb40, 
    mod=mod@entry=0x555555b73c00) at Python/compile.c:1836
#16 0x000055555569682b in PyAST_CompileObject (mod=mod@entry=0x555555b73c00, 
    filename=filename@entry=0x7ffff662a7b0, flags=flags@entry=0x7fffffffddc0, 
    optimize=optimize@entry=-1, arena=arena@entry=0x7ffff7e69640)
    at Python/compile.c:364
#17 0x00005555556c20cc in run_mod (mod=mod@entry=0x555555b73c00, 
    filename=filename@entry=0x7ffff662a7b0, 
    globals=globals@entry=0x7ffff7ecf3b0, locals=locals@entry=0x7ffff7ecf3b0, 
    flags=flags@entry=0x7fffffffddc0, arena=arena@entry=0x7ffff7e69640)
    at Python/pythonrun.c:1138
#18 0x00005555556c530c in PyRun_FileExFlags (fp=fp@entry=0x555555b6d000, 
    filename_str=filename_str@entry=0x7ffff7ecf720 "/home/asottile/workspace/cpython/t2.py", start=start@entry=257, globals=globals@entry=0x7ffff7ecf3b0, 
    locals=locals@entry=0x7ffff7ecf3b0, closeit=closeit@entry=1, 
    flags=0x7fffffffddc0) at Python/pythonrun.c:1063
#19 0x00005555556c56e6 in PyRun_SimpleFileExFlags (fp=fp@entry=0x555555b6d000, 
    filename=<optimized out>, 
    filename@entry=0x7ffff7ecf720 "/home/asottile/workspace/cpython/t2.py", 
    closeit=closeit@entry=1, flags=flags@entry=0x7fffffffddc0)
    at Python/pythonrun.c:428
#20 0x00005555556c58e9 in PyRun_AnyFileExFlags (fp=fp@entry=0x555555b6d000, 
    filename=0x7ffff7ecf720 "/home/asottile/workspace/cpython/t2.py", 
    closeit=closeit@entry=1, flags=flags@entry=0x7fffffffddc0)
    at Python/pythonrun.c:86
#21 0x00005555555aceca in pymain_run_file (config=config@entry=0x555555b2f190, 
    cf=cf@entry=0x7fffffffddc0) at Modules/main.c:369
#22 0x00005555555ad698 in pymain_run_python (
    exitcode=exitcode@entry=0x7fffffffddf4) at Modules/main.c:553
#23 0x00005555555ad703 in Py_RunMain () at Modules/main.c:632
#24 0x00005555555ad77d in pymain_main (args=args@entry=0x7fffffffde50)
    at Modules/main.c:662
#25 0x00005555555ad843 in Py_BytesMain (argc=<optimized out>, 
    argv=<optimized out>) at Modules/main.c:686
---Type <return> to continue, or q <return> to quit---
#26 0x00005555555ac053 in main (argc=<optimized out>, argv=<optimized out>)
    at ./Programs/python.c:16