Here is a more useful ASan report:

=================================================================
==12168==ERROR: AddressSanitizer: heap-use-after-free on address 0x62500001e110 at pc 0x000000697238 bp 0x7fff412b9240 sp 0x7fff412b9238
READ of size 1 at 0x62500001e110 thread T0
    #0 0x697237 in tok_nextc /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:911:20
    #1 0x68c63b in tok_get /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:1460:13
    #2 0x689d93 in PyTokenizer_Get /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:1809:18
    #3 0x67fec3 in parsetok /home/brian/src/fuzzpy/cpython/Parser/parsetok.c:208:16
    #4 0x6837d4 in PyParser_ParseFileObject /home/brian/src/fuzzpy/cpython/Parser/parsetok.c:134:12
    #5 0x52f50c in PyParser_ASTFromFileObject /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:1150:15
    #6 0x532e16 in PyRun_FileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:916:11
    #7 0x52c3f8 in PyRun_SimpleFileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:396:13
    #8 0x52a460 in PyRun_AnyFileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:80:16
    #9 0x5cb04a in run_file /home/brian/src/fuzzpy/cpython/Modules/main.c:318:11
    #10 0x5c5a42 in Py_Main /home/brian/src/fuzzpy/cpython/Modules/main.c:768:19
    #11 0x4fbace in main /home/brian/src/fuzzpy/cpython/./Programs/python.c:69:11
    #12 0x7fe8a9a4aa3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x20a3f)
    #13 0x431548 in _start (/home/brian/src/fuzzpy/cpython/python+0x431548)

0x62500001e110 is located 16 bytes inside of 8224-byte region [0x62500001e100,0x625000020120)
freed by thread T0 here:
    #0 0x4cdef0 in realloc /home/brian/src/fuzzpy/llvm_src/llvm/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:61
    #1 0x501280 in _PyMem_RawRealloc /home/brian/src/fuzzpy/cpython/Objects/obmalloc.c:84:12
    #2 0x4fc68d in _PyMem_DebugRealloc /home/brian/src/fuzzpy/cpython/Objects/obmalloc.c:1921:18
    #3 0x4fdf42 in PyMem_Realloc /home/brian/src/fuzzpy/cpython/Objects/obmalloc.c:343:12
    #4 0x69a338 in tok_nextc /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:1050:34
    #5 0x68a2c9 in tok_get /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:1357:17
    #6 0x689d93 in PyTokenizer_Get /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:1809:18
    #7 0x67fec3 in parsetok /home/brian/src/fuzzpy/cpython/Parser/parsetok.c:208:16
    #8 0x6837d4 in PyParser_ParseFileObject /home/brian/src/fuzzpy/cpython/Parser/parsetok.c:134:12
    #9 0x52f50c in PyParser_ASTFromFileObject /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:1150:15
    #10 0x532e16 in PyRun_FileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:916:11
    #11 0x52c3f8 in PyRun_SimpleFileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:396:13
    #12 0x52a460 in PyRun_AnyFileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:80:16
    #13 0x5cb04a in run_file /home/brian/src/fuzzpy/cpython/Modules/main.c:318:11
    #14 0x5c5a42 in Py_Main /home/brian/src/fuzzpy/cpython/Modules/main.c:768:19
    #15 0x4fbace in main /home/brian/src/fuzzpy/cpython/./Programs/python.c:69:11
    #16 0x7fe8a9a4aa3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x20a3f)

previously allocated by thread T0 here:
    #0 0x4cdb88 in malloc /home/brian/src/fuzzpy/llvm_src/llvm/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:40
    #1 0x501030 in _PyMem_RawMalloc /home/brian/src/fuzzpy/cpython/Objects/obmalloc.c:62:12
    #2 0x5074db in _PyMem_DebugAlloc /home/brian/src/fuzzpy/cpython/Objects/obmalloc.c:1838:22
    #3 0x4fc213 in _PyMem_DebugMalloc /home/brian/src/fuzzpy/cpython/Objects/obmalloc.c:1861:12
    #4 0x4fdbfa in PyMem_Malloc /home/brian/src/fuzzpy/cpython/Objects/obmalloc.c:325:12
    #5 0x68791d in PyTokenizer_FromFile /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:861:29
    #6 0x68359e in PyParser_ParseFileObject /home/brian/src/fuzzpy/cpython/Parser/parsetok.c:126:16
    #7 0x52f50c in PyParser_ASTFromFileObject /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:1150:15
    #8 0x532e16 in PyRun_FileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:916:11
    #9 0x52c3f8 in PyRun_SimpleFileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:396:13
    #10 0x52a460 in PyRun_AnyFileExFlags /home/brian/src/fuzzpy/cpython/Python/pythonrun.c:80:16
    #11 0x5cb04a in run_file /home/brian/src/fuzzpy/cpython/Modules/main.c:318:11
    #12 0x5c5a42 in Py_Main /home/brian/src/fuzzpy/cpython/Modules/main.c:768:19
    #13 0x4fbace in main /home/brian/src/fuzzpy/cpython/./Programs/python.c:69:11
    #14 0x7fe8a9a4aa3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x20a3f)

SUMMARY: AddressSanitizer: heap-use-after-free /home/brian/src/fuzzpy/cpython/Parser/tokenizer.c:911:20 in tok_nextc
Shadow bytes around the buggy address:
  0x0c4a7fffbbd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fffbbe0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fffbbf0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fffbc00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fffbc10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c4a7fffbc20: fd fd[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fffbc30: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fffbc40: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fffbc50: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fffbc60: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fffbc70: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==12168==ABORTING