Saya telah pemrograman selama lebih dari 9 tahun, dan menurut saran dari guru pemrograman pertama saya, saya selalu menjaga main()
fungsi saya sangat singkat.
Awalnya saya tidak tahu kenapa. Saya hanya patuh tanpa pengertian, sangat menyenangkan para profesor saya.
Setelah mendapatkan pengalaman, saya menyadari bahwa jika saya mendesain kode saya dengan benar, memiliki main()
fungsi pendek terjadi saja. Menulis kode termodulasi dan mengikuti prinsip tanggung jawab tunggal memungkinkan kode saya dirancang dalam "tandan", dan main()
berfungsi sebagai katalis untuk menjalankan program.
Maju cepat ke beberapa minggu yang lalu, saya melihat kode sumber Python, dan saya menemukan main()
fungsinya:
/* Minimal main program -- everything is loaded from the library */
...
int
main(int argc, char **argv)
{
...
return Py_Main(argc, argv);
}
Yay python. main()
Fungsi pendek == Kode yang baik.
Memprogram guru benar.
Ingin melihat lebih dalam, saya melihat Py_Main. Secara keseluruhan, didefinisikan sebagai berikut:
/* Main program */
int
Py_Main(int argc, char **argv)
{
int c;
int sts;
char *command = NULL;
char *filename = NULL;
char *module = NULL;
FILE *fp = stdin;
char *p;
int unbuffered = 0;
int skipfirstline = 0;
int stdin_is_interactive = 0;
int help = 0;
int version = 0;
int saw_unbuffered_flag = 0;
PyCompilerFlags cf;
cf.cf_flags = 0;
orig_argc = argc; /* For Py_GetArgcArgv() */
orig_argv = argv;
#ifdef RISCOS
Py_RISCOSWimpFlag = 0;
#endif
PySys_ResetWarnOptions();
while ((c = _PyOS_GetOpt(argc, argv, PROGRAM_OPTS)) != EOF) {
if (c == 'c') {
/* -c is the last option; following arguments
that look like options are left for the
command to interpret. */
command = (char *)malloc(strlen(_PyOS_optarg) + 2);
if (command == NULL)
Py_FatalError(
"not enough memory to copy -c argument");
strcpy(command, _PyOS_optarg);
strcat(command, "\n");
break;
}
if (c == 'm') {
/* -m is the last option; following arguments
that look like options are left for the
module to interpret. */
module = (char *)malloc(strlen(_PyOS_optarg) + 2);
if (module == NULL)
Py_FatalError(
"not enough memory to copy -m argument");
strcpy(module, _PyOS_optarg);
break;
}
switch (c) {
case 'b':
Py_BytesWarningFlag++;
break;
case 'd':
Py_DebugFlag++;
break;
case '3':
Py_Py3kWarningFlag++;
if (!Py_DivisionWarningFlag)
Py_DivisionWarningFlag = 1;
break;
case 'Q':
if (strcmp(_PyOS_optarg, "old") == 0) {
Py_DivisionWarningFlag = 0;
break;
}
if (strcmp(_PyOS_optarg, "warn") == 0) {
Py_DivisionWarningFlag = 1;
break;
}
if (strcmp(_PyOS_optarg, "warnall") == 0) {
Py_DivisionWarningFlag = 2;
break;
}
if (strcmp(_PyOS_optarg, "new") == 0) {
/* This only affects __main__ */
cf.cf_flags |= CO_FUTURE_DIVISION;
/* And this tells the eval loop to treat
BINARY_DIVIDE as BINARY_TRUE_DIVIDE */
_Py_QnewFlag = 1;
break;
}
fprintf(stderr,
"-Q option should be `-Qold', "
"`-Qwarn', `-Qwarnall', or `-Qnew' only\n");
return usage(2, argv[0]);
/* NOTREACHED */
case 'i':
Py_InspectFlag++;
Py_InteractiveFlag++;
break;
/* case 'J': reserved for Jython */
case 'O':
Py_OptimizeFlag++;
break;
case 'B':
Py_DontWriteBytecodeFlag++;
break;
case 's':
Py_NoUserSiteDirectory++;
break;
case 'S':
Py_NoSiteFlag++;
break;
case 'E':
Py_IgnoreEnvironmentFlag++;
break;
case 't':
Py_TabcheckFlag++;
break;
case 'u':
unbuffered++;
saw_unbuffered_flag = 1;
break;
case 'v':
Py_VerboseFlag++;
break;
#ifdef RISCOS
case 'w':
Py_RISCOSWimpFlag = 1;
break;
#endif
case 'x':
skipfirstline = 1;
break;
/* case 'X': reserved for implementation-specific arguments */
case 'U':
Py_UnicodeFlag++;
break;
case 'h':
case '?':
help++;
break;
case 'V':
version++;
break;
case 'W':
PySys_AddWarnOption(_PyOS_optarg);
break;
/* This space reserved for other options */
default:
return usage(2, argv[0]);
/*NOTREACHED*/
}
}
if (help)
return usage(0, argv[0]);
if (version) {
fprintf(stderr, "Python %s\n", PY_VERSION);
return 0;
}
if (Py_Py3kWarningFlag && !Py_TabcheckFlag)
/* -3 implies -t (but not -tt) */
Py_TabcheckFlag = 1;
if (!Py_InspectFlag &&
(p = Py_GETENV("PYTHONINSPECT")) && *p != '\0')
Py_InspectFlag = 1;
if (!saw_unbuffered_flag &&
(p = Py_GETENV("PYTHONUNBUFFERED")) && *p != '\0')
unbuffered = 1;
if (!Py_NoUserSiteDirectory &&
(p = Py_GETENV("PYTHONNOUSERSITE")) && *p != '\0')
Py_NoUserSiteDirectory = 1;
if ((p = Py_GETENV("PYTHONWARNINGS")) && *p != '\0') {
char *buf, *warning;
buf = (char *)malloc(strlen(p) + 1);
if (buf == NULL)
Py_FatalError(
"not enough memory to copy PYTHONWARNINGS");
strcpy(buf, p);
for (warning = strtok(buf, ",");
warning != NULL;
warning = strtok(NULL, ","))
PySys_AddWarnOption(warning);
free(buf);
}
if (command == NULL && module == NULL && _PyOS_optind < argc &&
strcmp(argv[_PyOS_optind], "-") != 0)
{
#ifdef __VMS
filename = decc$translate_vms(argv[_PyOS_optind]);
if (filename == (char *)0 || filename == (char *)-1)
filename = argv[_PyOS_optind];
#else
filename = argv[_PyOS_optind];
#endif
}
stdin_is_interactive = Py_FdIsInteractive(stdin, (char *)0);
if (unbuffered) {
#if defined(MS_WINDOWS) || defined(__CYGWIN__)
_setmode(fileno(stdin), O_BINARY);
_setmode(fileno(stdout), O_BINARY);
#endif
#ifdef HAVE_SETVBUF
setvbuf(stdin, (char *)NULL, _IONBF, BUFSIZ);
setvbuf(stdout, (char *)NULL, _IONBF, BUFSIZ);
setvbuf(stderr, (char *)NULL, _IONBF, BUFSIZ);
#else /* !HAVE_SETVBUF */
setbuf(stdin, (char *)NULL);
setbuf(stdout, (char *)NULL);
setbuf(stderr, (char *)NULL);
#endif /* !HAVE_SETVBUF */
}
else if (Py_InteractiveFlag) {
#ifdef MS_WINDOWS
/* Doesn't have to have line-buffered -- use unbuffered */
/* Any set[v]buf(stdin, ...) screws up Tkinter :-( */
setvbuf(stdout, (char *)NULL, _IONBF, BUFSIZ);
#else /* !MS_WINDOWS */
#ifdef HAVE_SETVBUF
setvbuf(stdin, (char *)NULL, _IOLBF, BUFSIZ);
setvbuf(stdout, (char *)NULL, _IOLBF, BUFSIZ);
#endif /* HAVE_SETVBUF */
#endif /* !MS_WINDOWS */
/* Leave stderr alone - it should be unbuffered anyway. */
}
#ifdef __VMS
else {
setvbuf (stdout, (char *)NULL, _IOLBF, BUFSIZ);
}
#endif /* __VMS */
#ifdef __APPLE__
/* On MacOS X, when the Python interpreter is embedded in an
application bundle, it gets executed by a bootstrapping script
that does os.execve() with an argv[0] that's different from the
actual Python executable. This is needed to keep the Finder happy,
or rather, to work around Apple's overly strict requirements of
the process name. However, we still need a usable sys.executable,
so the actual executable path is passed in an environment variable.
See Lib/plat-mac/bundlebuiler.py for details about the bootstrap
script. */
if ((p = Py_GETENV("PYTHONEXECUTABLE")) && *p != '\0')
Py_SetProgramName(p);
else
Py_SetProgramName(argv[0]);
#else
Py_SetProgramName(argv[0]);
#endif
Py_Initialize();
if (Py_VerboseFlag ||
(command == NULL && filename == NULL && module == NULL && stdin_is_interactive)) {
fprintf(stderr, "Python %s on %s\n",
Py_GetVersion(), Py_GetPlatform());
if (!Py_NoSiteFlag)
fprintf(stderr, "%s\n", COPYRIGHT);
}
if (command != NULL) {
/* Backup _PyOS_optind and force sys.argv[0] = '-c' */
_PyOS_optind--;
argv[_PyOS_optind] = "-c";
}
if (module != NULL) {
/* Backup _PyOS_optind and force sys.argv[0] = '-c'
so that PySys_SetArgv correctly sets sys.path[0] to ''
rather than looking for a file called "-m". See
tracker issue #8202 for details. */
_PyOS_optind--;
argv[_PyOS_optind] = "-c";
}
PySys_SetArgv(argc-_PyOS_optind, argv+_PyOS_optind);
if ((Py_InspectFlag || (command == NULL && filename == NULL && module == NULL)) &&
isatty(fileno(stdin))) {
PyObject *v;
v = PyImport_ImportModule("readline");
if (v == NULL)
PyErr_Clear();
else
Py_DECREF(v);
}
if (command) {
sts = PyRun_SimpleStringFlags(command, &cf) != 0;
free(command);
} else if (module) {
sts = RunModule(module, 1);
free(module);
}
else {
if (filename == NULL && stdin_is_interactive) {
Py_InspectFlag = 0; /* do exit on SystemExit */
RunStartupFile(&cf);
}
/* XXX */
sts = -1; /* keep track of whether we've already run __main__ */
if (filename != NULL) {
sts = RunMainFromImporter(filename);
}
if (sts==-1 && filename!=NULL) {
if ((fp = fopen(filename, "r")) == NULL) {
fprintf(stderr, "%s: can't open file '%s': [Errno %d] %s\n",
argv[0], filename, errno, strerror(errno));
return 2;
}
else if (skipfirstline) {
int ch;
/* Push back first newline so line numbers
remain the same */
while ((ch = getc(fp)) != EOF) {
if (ch == '\n') {
(void)ungetc(ch, fp);
break;
}
}
}
{
/* XXX: does this work on Win/Win64? (see posix_fstat) */
struct stat sb;
if (fstat(fileno(fp), &sb) == 0 &&
S_ISDIR(sb.st_mode)) {
fprintf(stderr, "%s: '%s' is a directory, cannot continue\n", argv[0], filename);
fclose(fp);
return 1;
}
}
}
if (sts==-1) {
/* call pending calls like signal handlers (SIGINT) */
if (Py_MakePendingCalls() == -1) {
PyErr_Print();
sts = 1;
} else {
sts = PyRun_AnyFileExFlags(
fp,
filename == NULL ? "<stdin>" : filename,
filename != NULL, &cf) != 0;
}
}
}
/* Check this environment variable at the end, to give programs the
* opportunity to set it from Python.
*/
if (!Py_InspectFlag &&
(p = Py_GETENV("PYTHONINSPECT")) && *p != '\0')
{
Py_InspectFlag = 1;
}
if (Py_InspectFlag && stdin_is_interactive &&
(filename != NULL || command != NULL || module != NULL)) {
Py_InspectFlag = 0;
/* XXX */
sts = PyRun_AnyFileFlags(stdin, "<stdin>", &cf) != 0;
}
Py_Finalize();
#ifdef RISCOS
if (Py_RISCOSWimpFlag)
fprintf(stderr, "\x0cq\x0c"); /* make frontend quit */
#endif
#ifdef __INSURE__
/* Insure++ is a memory analysis tool that aids in discovering
* memory leaks and other memory problems. On Python exit, the
* interned string dictionary is flagged as being in use at exit
* (which it is). Under normal circumstances, this is fine because
* the memory will be automatically reclaimed by the system. Under
* memory debugging, it's a huge source of useless noise, so we
* trade off slower shutdown for less distraction in the memory
* reports. -baw
*/
_Py_ReleaseInternedStrings();
#endif /* __INSURE__ */
return sts;
}
Ya Tuhan Yang Maha Kuasa ... itu cukup besar untuk menenggelamkan Titanic.
Tampaknya seolah-olah Python melakukan trik "Pengenalan Pemrograman 101" dan baru saja memindahkan semua main()
kode ke fungsi yang berbeda, menyebutnya sesuatu yang sangat mirip dengan "utama".
Inilah pertanyaan saya: Apakah kode ini ditulis dengan sangat buruk, atau adakah alasan lain untuk memiliki fungsi utama yang singkat?
Seperti berdiri sekarang, saya sama sekali tidak melihat perbedaan antara melakukan ini dan hanya memindahkan kode Py_Main()
kembali ke main()
. Apakah saya salah dalam memikirkan ini?
options = ParseOptionFlags(argc,argv)
mana options
adalah struct
yang berisi variabel Py_BytesWarningFlag
, Py_DebugFlag
, dll ...