/in/foo.c:1:1: error: unknown type name 'def'
    1 | def prime_factors():
      | ^~~
/in/foo.c: In function 'prime_factors':
/in/foo.c:1:20: error: expected declaration specifiers before ':' token
    1 | def prime_factors():
      |                    ^
/in/foo.c:20:14: error: stray '#' in program
   20 |     print()  # 换行
      |              ^
/in/foo.c:23: warning: control reaches end of non-void function [-Wreturn-type]