src.c:1:1: error: unknown type name 'def'
def fun(a,n):
^
src.c: In function 'fun':
src.c:1:13: error: expected declaration specifiers before ':' token
def fun(a,n):
^
src.c:4:5: error: expected declaration specifiers before 'return'
return a*fun(a,n-1)
^