struct.calcsize('iiiii?') : 21

appears to be incorrect ; in C sizeof : 24

C code:
typedef struct {
  int	param1;
  int	param2;
  int	param3;
  int	param4;
  int	param5;
  unsigned char param6;
} struct_titi6;

main:
struct_titi6 toto3;
printf("taille toto3 : %d\n",sizeof(toto3));
printf("taille toto3.param1 : %d\n",sizeof(toto3.param1));
printf("taille toto3.param6 : %d\n",sizeof(toto3.param6));

results:
taille toto3 : 24
taille toto3.param1 : 4
taille toto3.param6 : 1