GeezerVison

>>> class a: [a for a in [b] for b[[b for _ in [] if a if b]] in [2]]
... 
SystemError: compiler_lookup_arg(name='a') with reftype=1 failed in <module>; freevars of code a: ('a',)

>>> class C: [a for a in [] if [a for _ in []]]
... 
SystemError: _PyST_GetScope(name='a') failed: unknown scope in unit <module> (5033699440); symbols: {'C': 2050}; locals: {}; globals: {}

class a:
    def a():
        class a:
            [(lambda : (a := a[(a := 2)])[b]) for b in (lambda b, a: 7)[a]]
            [][2] = b
            (1)[lambda a: a] = 4
            (2)[2] = b = a
        (4)[lambda b, a: b] = a = lambda : 1

* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x8)
  * frame #0: 0x000000010008b33c python.exe`Py_TYPE(ob=0x0000000000000000) at object.h:204:16 [opt]
    frame #1: 0x000000010008ca8c python.exe`Py_IS_TYPE(ob=<unavailable>, type=0x000000010042d148) at object.h:235:12 [opt]
    frame #2: 0x000000010008db38 python.exe`_PyCode_ConstantKey(op=0x0000000000000000) at codeobject.c:2163:11 [opt]
    frame #3: 0x000000010008dd00 python.exe`_PyCode_ConstantKey(op=0x0000000103557a70) at codeobject.c:2225:24 [opt]
    frame #4: 0x0000000100173334 python.exe`_PyCompile_ConstCacheMergeOne(const_cache=0x0000000103023890, obj=0x000000016fdfedd8) at compile.c:7380:21 [opt]
    frame #5: 0x000000010014d88c python.exe`makecode(umd=0x0000000103407bb0, a=0x000000016fdfee50, const_cache=0x0000000103023890, constslist=0x000000010354b750, maxdepth=5, nlocalsplus=2, code_flags=0, filename=0x0000000103077e20) at assemble.c:569:9 [opt]
    frame #6: 0x000000010014d5b8 python.exe`_PyAssemble_MakeCodeObject(umd=0x0000000103407bb0, const_cache=0x0000000103023890, consts=0x000000010354b750, maxdepth=5, instrs=<unavailable>, nlocalsplus=2, code_flags=0, filename=0x0000000103077e20) at assemble.c:598:14 [opt]

def a():
    class a:
        [(lambda : b) for b in [a]]
        print(b)

def a():
    def a():
        [(lambda : b) for b in [a]]
        print(b)