/in/foo.c:1:1: error: unknown type name 'def'
    1 | def prime_factors(n):
      | ^~~
/in/foo.c: In function 'prime_factors':
/in/foo.c:1:21: error: expected declaration specifiers before ':' token
    1 | def prime_factors(n):
      |                     ^
/in/foo.c:1:5: warning: type of 'n' defaults to 'int' [-Wimplicit-int]
    1 | def prime_factors(n):
      |     ^~~~~~~~~~~~~
/in/foo.c:24: warning: control reaches end of non-void function [-Wreturn-type]