Valgrind can also complain:

valgrind --leak-check=yes --suppressions=Misc/valgrind-python.supp Parser/pgen ./Grammar/Grammar Include/graminit.h Python/graminit.c
==6836== Memcheck, a memory error detector
==6836== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==6836== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==6836== Command: Parser/pgen ./Grammar/Grammar Include/graminit.h Python/graminit.c
==6836== 
Translating labels ...
==6836== 
==6836== HEAP SUMMARY:
==6836==     in use at exit: 18,236 bytes in 133 blocks
==6836==   total heap usage: 848 allocs, 715 frees, 781,340 bytes allocated
==6836== 
==6836== 6 bytes in 1 blocks are possibly lost in loss record 1 of 11
==6836==    at 0x4C2BBCF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x50E1379: strdup (strdup.c:42)
==6836==    by 0x403405: _Py_addlabel (grammar.c:104)
==6836==    by 0x403D40: newnfagrammar (pgen.c:116)
==6836==    by 0x403E21: metacompile (pgen.c:158)
==6836==    by 0x4056F1: _Py_pgen (pgen.c:668)
==6836==    by 0x40CBE3: getgrammar (pgenmain.c:125)
==6836==    by 0x40C932: main (pgenmain.c:64)
==6836== 
==6836== 178 bytes in 33 blocks are possibly lost in loss record 2 of 11
==6836==    at 0x4C2BBCF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x403838: translabel (grammar.c:203)
==6836==    by 0x40356A: _Py_translatelabels (grammar.c:147)
==6836==    by 0x405711: _Py_pgen (pgen.c:670)
==6836==    by 0x40CBE3: getgrammar (pgenmain.c:125)
==6836==    by 0x40C932: main (pgenmain.c:64)
==6836== 
==6836== 584 bytes in 1 blocks are possibly lost in loss record 3 of 11
==6836==    at 0x4C2BBCF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x405774: _PyMem_RawMalloc (obmalloc.c:83)
==6836==    by 0x4076DE: _PyMem_DebugRawAlloc (obmalloc.c:1903)
==6836==    by 0x4077CC: _PyMem_DebugRawMalloc (obmalloc.c:1926)
==6836==    by 0x405EDF: PyMem_RawMalloc (obmalloc.c:396)
==6836==    by 0x406D16: _PyObject_Alloc (obmalloc.c:1466)
==6836==    by 0x407515: _PyObject_Realloc (obmalloc.c:1756)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x407BB2: _PyMem_DebugRealloc (obmalloc.c:2049)
==6836==    by 0x40620A: PyObject_Realloc (obmalloc.c:507)
==6836==    by 0x4030C6: _Py_addstate (grammar.c:55)
==6836==    by 0x405497: convert (pgen.c:611)
==6836== 
==6836== 640 bytes in 1 blocks are possibly lost in loss record 4 of 11
==6836==    at 0x4C2DD9F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x4057F3: _PyMem_RawRealloc (obmalloc.c:105)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x405F70: PyMem_RawRealloc (obmalloc.c:414)
==6836==    by 0x40756A: _PyObject_Realloc (obmalloc.c:1777)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x407BB2: _PyMem_DebugRealloc (obmalloc.c:2049)
==6836==    by 0x40620A: PyObject_Realloc (obmalloc.c:507)
==6836==    by 0x403B2A: addnfastate (pgen.c:52)
==6836==    by 0x4047E5: compile_atom (pgen.c:300)
==6836==    by 0x4045E9: compile_item (pgen.c:268)
==6836==    by 0x40438D: compile_alt (pgen.c:237)
==6836== 
==6836== 744 bytes in 1 blocks are definitely lost in loss record 5 of 11
==6836==    at 0x4C2DD9F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x4057F3: _PyMem_RawRealloc (obmalloc.c:105)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x405F70: PyMem_RawRealloc (obmalloc.c:414)
==6836==    by 0x40756A: _PyObject_Realloc (obmalloc.c:1777)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x407BB2: _PyMem_DebugRealloc (obmalloc.c:2049)
==6836==    by 0x40620A: PyObject_Realloc (obmalloc.c:507)
==6836==    by 0x403D8C: addnfa (pgen.c:126)
==6836==    by 0x403F4E: compile_rule (pgen.c:178)
==6836==    by 0x403E86: metacompile (pgen.c:164)
==6836==    by 0x4056F1: _Py_pgen (pgen.c:668)
==6836== 
==6836== 800 bytes in 1 blocks are possibly lost in loss record 6 of 11
==6836==    at 0x4C2BBCF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x405774: _PyMem_RawMalloc (obmalloc.c:83)
==6836==    by 0x4076DE: _PyMem_DebugRawAlloc (obmalloc.c:1903)
==6836==    by 0x407914: _PyMem_DebugRawRealloc (obmalloc.c:1971)
==6836==    by 0x405F70: PyMem_RawRealloc (obmalloc.c:414)
==6836==    by 0x40631C: new_arena (obmalloc.c:1064)
==6836==    by 0x4067FC: _PyObject_Alloc (obmalloc.c:1339)
==6836==    by 0x406D66: _PyObject_Malloc (obmalloc.c:1476)
==6836==    by 0x4076DE: _PyMem_DebugRawAlloc (obmalloc.c:1903)
==6836==    by 0x4077CC: _PyMem_DebugRawMalloc (obmalloc.c:1926)
==6836==    by 0x407B23: _PyMem_DebugMalloc (obmalloc.c:2028)
==6836==    by 0x406179: PyObject_Malloc (obmalloc.c:489)
==6836== 
==6836== 892 bytes in 85 blocks are possibly lost in loss record 7 of 11
==6836==    at 0x4C2BBCF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x50E1379: strdup (strdup.c:42)
==6836==    by 0x40304A: _Py_adddfa (grammar.c:42)
==6836==    by 0x405691: maketables (pgen.c:655)
==6836==    by 0x405701: _Py_pgen (pgen.c:669)
==6836==    by 0x40CBE3: getgrammar (pgenmain.c:125)
==6836==    by 0x40C932: main (pgenmain.c:64)
==6836== 
==6836== 2,272 bytes in 3 blocks are possibly lost in loss record 8 of 11
==6836==    at 0x4C2DD9F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x4057F3: _PyMem_RawRealloc (obmalloc.c:105)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x405F70: PyMem_RawRealloc (obmalloc.c:414)
==6836==    by 0x40756A: _PyObject_Realloc (obmalloc.c:1777)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x407BB2: _PyMem_DebugRealloc (obmalloc.c:2049)
==6836==    by 0x40620A: PyObject_Realloc (obmalloc.c:507)
==6836==    by 0x4030C6: _Py_addstate (grammar.c:55)
==6836==    by 0x405497: convert (pgen.c:611)
==6836==    by 0x404F7B: makedfa (pgen.c:489)
==6836==    by 0x4056C0: maketables (pgen.c:656)
==6836== 
==6836== 2,864 bytes in 1 blocks are possibly lost in loss record 9 of 11
==6836==    at 0x4C2DD9F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x4057F3: _PyMem_RawRealloc (obmalloc.c:105)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x405F70: PyMem_RawRealloc (obmalloc.c:414)
==6836==    by 0x40756A: _PyObject_Realloc (obmalloc.c:1777)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x407BB2: _PyMem_DebugRealloc (obmalloc.c:2049)
==6836==    by 0x40620A: PyObject_Realloc (obmalloc.c:507)
==6836==    by 0x4033AA: _Py_addlabel (grammar.c:98)
==6836==    by 0x40480D: compile_atom (pgen.c:301)
==6836==    by 0x4045E9: compile_item (pgen.c:268)
==6836==    by 0x40433D: compile_alt (pgen.c:232)
==6836== 
==6836== 3,464 bytes in 1 blocks are possibly lost in loss record 10 of 11
==6836==    at 0x4C2DD9F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x4057F3: _PyMem_RawRealloc (obmalloc.c:105)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x405F70: PyMem_RawRealloc (obmalloc.c:414)
==6836==    by 0x40756A: _PyObject_Realloc (obmalloc.c:1777)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x407BB2: _PyMem_DebugRealloc (obmalloc.c:2049)
==6836==    by 0x40620A: PyObject_Realloc (obmalloc.c:507)
==6836==    by 0x402FE4: _Py_adddfa (grammar.c:36)
==6836==    by 0x405691: maketables (pgen.c:655)
==6836==    by 0x405701: _Py_pgen (pgen.c:669)
==6836==    by 0x40CBE3: getgrammar (pgenmain.c:125)
==6836== 
==6836== 5,792 bytes in 5 blocks are possibly lost in loss record 11 of 11
==6836==    at 0x4C2DD9F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6836==    by 0x4057F3: _PyMem_RawRealloc (obmalloc.c:105)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x405F70: PyMem_RawRealloc (obmalloc.c:414)
==6836==    by 0x40756A: _PyObject_Realloc (obmalloc.c:1777)
==6836==    by 0x407999: _PyMem_DebugRawRealloc (obmalloc.c:1986)
==6836==    by 0x407BB2: _PyMem_DebugRealloc (obmalloc.c:2049)
==6836==    by 0x40620A: PyObject_Realloc (obmalloc.c:507)
==6836==    by 0x403B2A: addnfastate (pgen.c:52)
==6836==    by 0x4047E5: compile_atom (pgen.c:300)
==6836==    by 0x4045E9: compile_item (pgen.c:268)
==6836==    by 0x40433D: compile_alt (pgen.c:232)
==6836== 
==6836== LEAK SUMMARY:
==6836==    definitely lost: 744 bytes in 1 blocks
==6836==    indirectly lost: 0 bytes in 0 blocks
==6836==      possibly lost: 17,492 bytes in 132 blocks
==6836==    still reachable: 0 bytes in 0 blocks
==6836==         suppressed: 0 bytes in 0 blocks
==6836== 
==6836== For counts of detected and suppressed errors, rerun with: -v
==6836== ERROR SUMMARY: 11 errors from 11 contexts (suppressed: 484 from 2)