PC/getpathp.c

   1
   2 /* Return the initial module search path. */
   3 /* Used by DOS, OS/2, Windows 3.1, Windows 95/98, Windows NT. */
   4
   5 /* ----------------------------------------------------------------
   6    PATH RULES FOR WINDOWS:
   7    This describes how sys.path is formed on Windows.  It describes the
   8    functionality, not the implementation (ie, the order in which these
   9    are actually fetched is different)
  10
  11    * Python always adds an empty entry at the start, which corresponds
  12      to the current directory.
  13
  14    * If the PYTHONPATH env. var. exists, its entries are added next.
  15
  16    * We look in the registry for "application paths" - that is, sub-keys
  17      under the main PythonPath registry key.  These are added next (the
  18      order of sub-key processing is undefined).
  19      HKEY_CURRENT_USER is searched and added first.
  20      HKEY_LOCAL_MACHINE is searched and added next.
  21      (Note that all known installers only use HKLM, so HKCU is typically
  22      empty)
  23
  24    * We attempt to locate the "Python Home" - if the PYTHONHOME env var
  25      is set, we believe it.  Otherwise, we use the path of our host .EXE's
  26      to try and locate our "landmark" (lib\\os.py) and deduce our home.
  27      - If we DO have a Python Home: The relevant sub-directories (Lib,
  28        plat-win, lib-tk, etc) are based on the Python Home
  29      - If we DO NOT have a Python Home, the core Python Path is
  30        loaded from the registry.  This is the main PythonPath key,
  31        and both HKLM and HKCU are combined to form the path)
  32
  33    * Iff - we can not locate the Python Home, have not had a PYTHONPATH
  34      specified, and can't locate any Registry entries (ie, we have _nothing_
  35      we can assume is a good path), a default path with relative entries is
  36      used (eg. .\Lib;.\plat-win, etc)
  37
  38
  39   The end result of all this is:
  40   * When running python.exe, or any other .exe in the main Python directory
  41     (either an installed version, or directly from the PCbuild directory),
  42     the core path is deduced, and the core paths in the registry are
  43     ignored.  Other "application paths" in the registry are always read.
  44
  45   * When Python is hosted in another exe (different directory, embedded via
  46     COM, etc), the Python Home will not be deduced, so the core path from
  47     the registry is used.  Other "application paths" in the registry are
  48     always read.
  49
  50   * If Python can't find its home and there is no registry (eg, frozen
  51     exe, some very strange installation setup) you get a path with
  52     some default, but relative, paths.
  53
  54    ---------------------------------------------------------------- */
  55
  56
  57 #include "Python.h"
  58 #include "osdefs.h"
  59
  60 #ifdef MS_WINDOWS
  61 #include <windows.h>
  62 #include <tchar.h>
  63 #endif
  64
  65 #ifdef HAVE_SYS_TYPES_H
  66 #include <sys/types.h>
  67 #endif /* HAVE_SYS_TYPES_H */
  68
  69 #ifdef HAVE_SYS_STAT_H
  70 #include <sys/stat.h>
  71 #endif /* HAVE_SYS_STAT_H */
  72
  73 #include <string.h>
  74
  75 /* Search in some common locations for the associated Python libraries.
  76  *
  77  * Py_GetPath() tries to return a sensible Python module search path.
  78  *
  79  * The approach is an adaptation for Windows of the strategy used in
  80  * ../Modules/getpath.c; it uses the Windows Registry as one of its
  81  * information sources.
  82  */
  83
  84 #ifndef LANDMARK
  85 #define LANDMARK "lib\\os.py"
  86 #endif
  87
  88 static char prefix[MAXPATHLEN+1];
  89 static char progpath[MAXPATHLEN+1];
  90 static char dllpath[MAXPATHLEN+1];
  91 static char *module_search_path = NULL;
  92
  93
  94 static int
  95 is_sep(char ch) /* determine if "ch" is a separator character */
  96 {
  97 #ifdef ALTSEP
  98         return ch == SEP || ch == ALTSEP;
  99 #else
 100         return ch == SEP;
 101 #endif
 102 }
 103
 104 /* assumes 'dir' null terminated in bounds.  Never writes
 105    beyond existing terminator.
 106 */
 107 static void
 108 reduce(char *dir)
 109 {
 110         size_t i = strlen(dir);
 111         while (i > 0 && !is_sep(dir[i]))
 112                 --i;
 113         dir[i] = '\0';
 114 }
 115
 116
 117 static int
 118 exists(char *filename)
 119 {
 120         struct stat buf;
 121         return stat(filename, &buf) == 0;
 122 }
 123
 124 /* Assumes 'filename' MAXPATHLEN+1 bytes long -
 125    may extend 'filename' by one character.
 126 */
 127 static int
 128 ismodule(char *filename)        /* Is module -- check for .pyc/.pyo too */
 129 {
 130         if (exists(filename))
 131                 return 1;
 132
 133         /* Check for the compiled version of prefix. */
 134         if (strlen(filename) < MAXPATHLEN) {
 135                 strcat(filename, Py_OptimizeFlag ? "o" : "c");
 136                 if (exists(filename))
 137                         return 1;
 138         }
 139         return 0;
 140 }
 141
 142 /* Add a path component, by appending stuff to buffer.
 143    buffer must have at least MAXPATHLEN + 1 bytes allocated, and contain a
 144    NUL-terminated string with no more than MAXPATHLEN characters (not counting
 145    the trailing NUL).  It's a fatal error if it contains a string longer than
 146    that (callers must be careful!).  If these requirements are met, it's
 147    guaranteed that buffer will still be a NUL-terminated string with no more
 148    than MAXPATHLEN characters at exit.  If stuff is too long, only as much of
 149    stuff as fits will be appended.
 150 */
 151 static void
 152 join(char *buffer, char *stuff)
 153 {
 154         size_t n, k;
 155         if (is_sep(stuff[0]))
 156                 n = 0;
 157         else {
 158                 n = strlen(buffer);
 159                 if (n > 0 && !is_sep(buffer[n-1]) && n < MAXPATHLEN)
 160                         buffer[n++] = SEP;
 161         }
 162         if (n > MAXPATHLEN)
 163                 Py_FatalError("buffer overflow in getpathp.c's joinpath()");
 164         k = strlen(stuff);
 165         if (n + k > MAXPATHLEN)
 166                 k = MAXPATHLEN - n;
 167         strncpy(buffer+n, stuff, k);
 168         buffer[n+k] = '\0';
 169 }
 170
 171 /* gotlandmark only called by search_for_prefix, which ensures
 172    'prefix' is null terminated in bounds.  join() ensures
 173    'landmark' can not overflow prefix if too long.
 174 */
 175 static int
 176 gotlandmark(char *landmark)
 177 {
 178         int ok;
 179         Py_ssize_t n;
 180
 181         n = strlen(prefix);
 182         join(prefix, landmark);
 183         ok = ismodule(prefix);
 184         prefix[n] = '\0';
 185         return ok;
 186 }
 187
 188 /* assumes argv0_path is MAXPATHLEN+1 bytes long, already \0 term'd.
 189    assumption provided by only caller, calculate_path() */
 190 static int
 191 search_for_prefix(char *argv0_path, char *landmark)
 192 {
 193         /* Search from argv0_path, until landmark is found */
 194         strcpy(prefix, argv0_path);
 195         do {
 196                 if (gotlandmark(landmark))
 197                         return 1;
 198                 reduce(prefix);
 199         } while (prefix[0]);
 200         return 0;
 201 }
 202
 203 #ifdef MS_WINDOWS
 204
 205 /* a string loaded from the DLL at startup.*/
 206 extern const char *PyWin_DLLVersionString;
 207
 208
 209 /* Load a PYTHONPATH value from the registry.
 210    Load from either HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER.
 211
 212    Works in both Unicode and 8bit environments.  Only uses the
 213    Ex family of functions so it also works with Windows CE.
 214
 215    Returns NULL, or a pointer that should be freed.
 216
 217    XXX - this code is pretty strange, as it used to also
 218    work on Win16, where the buffer sizes werent available
 219    in advance.  It could be simplied now Win16/Win32s is dead!
 220 */
 221
 222 static char *
 223 getpythonregpath(HKEY keyBase, int skipcore)
 224 {
 225         HKEY newKey = 0;
 226         DWORD dataSize = 0;
 227         DWORD numKeys = 0;
 228         LONG rc;
 229         char *retval = NULL;
 230         TCHAR *dataBuf = NULL;
 231         static const TCHAR keyPrefix[] = _T("Software\\Python\\PythonCore\\");
 232         static const TCHAR keySuffix[] = _T("\\PythonPath");
 233         size_t versionLen;
 234         DWORD index;
 235         TCHAR *keyBuf = NULL;
 236         TCHAR *keyBufPtr;
 237         TCHAR **ppPaths = NULL;
 238
 239         /* Tried to use sysget("winver") but here is too early :-( */
 240         versionLen = _tcslen(PyWin_DLLVersionString);
 241         /* Space for all the chars, plus one \0 */
 242         keyBuf = keyBufPtr = malloc(sizeof(keyPrefix) +
 243                                     sizeof(TCHAR)*(versionLen-1) +
 244                                     sizeof(keySuffix));
 245         if (keyBuf==NULL) goto done;
 246
 247         memcpy(keyBufPtr, keyPrefix, sizeof(keyPrefix)-sizeof(TCHAR));
 248         keyBufPtr += sizeof(keyPrefix)/sizeof(TCHAR) - 1;
 249         memcpy(keyBufPtr, PyWin_DLLVersionString, versionLen * sizeof(TCHAR));
 250         keyBufPtr += versionLen;
 251         /* NULL comes with this one! */
 252         memcpy(keyBufPtr, keySuffix, sizeof(keySuffix));
 253         /* Open the root Python key */
 254         rc=RegOpenKeyEx(keyBase,
 255                         keyBuf, /* subkey */
 256                         0, /* reserved */
 257                         KEY_READ,
 258                         &newKey);
 259         if (rc!=ERROR_SUCCESS) goto done;
 260         /* Find out how big our core buffer is, and how many subkeys we have */
 261         rc = RegQueryInfoKey(newKey, NULL, NULL, NULL, &numKeys, NULL, NULL,
 262                         NULL, NULL, &dataSize, NULL, NULL);
 263         if (rc!=ERROR_SUCCESS) goto done;
 264         if (skipcore) dataSize = 0; /* Only count core ones if we want them! */
 265         /* Allocate a temp array of char buffers, so we only need to loop
 266            reading the registry once
 267         */
 268         ppPaths = malloc( sizeof(TCHAR *) * numKeys );
 269         if (ppPaths==NULL) goto done;
 270         memset(ppPaths, 0, sizeof(TCHAR *) * numKeys);
 271         /* Loop over all subkeys, allocating a temp sub-buffer. */
 272         for(index=0;index<numKeys;index++) {
 273                 TCHAR keyBuf[MAX_PATH+1];
 274                 HKEY subKey = 0;
 275                 DWORD reqdSize = MAX_PATH+1;
 276                 /* Get the sub-key name */
 277                 DWORD rc = RegEnumKeyEx(newKey, index, keyBuf, &reqdSize,
 278                                         NULL, NULL, NULL, NULL );
 279                 if (rc!=ERROR_SUCCESS) goto done;
 280                 /* Open the sub-key */
 281                 rc=RegOpenKeyEx(newKey,
 282                                                 keyBuf, /* subkey */
 283                                                 0, /* reserved */
 284                                                 KEY_READ,
 285                                                 &subKey);
 286                 if (rc!=ERROR_SUCCESS) goto done;
 287                 /* Find the value of the buffer size, malloc, then read it */
 288                 RegQueryValueEx(subKey, NULL, 0, NULL, NULL, &reqdSize);
 289                 if (reqdSize) {
 290                         ppPaths[index] = malloc(reqdSize);
 291                         if (ppPaths[index]) {
 292                                 RegQueryValueEx(subKey, NULL, 0, NULL,
 293                                                 (LPBYTE)ppPaths[index],
 294                                                 &reqdSize);
 295                                 dataSize += reqdSize + 1; /* 1 for the ";" */
 296                         }
 297                 }
 298                 RegCloseKey(subKey);
 299         }
 300         /* original datasize from RegQueryInfo doesn't include the \0 */
 301         dataBuf = malloc((dataSize+1) * sizeof(TCHAR));
 302         if (dataBuf) {
 303                 TCHAR *szCur = dataBuf;
 304                 DWORD reqdSize = dataSize;
 305                 /* Copy our collected strings */
 306                 for (index=0;index<numKeys;index++) {
 307                         if (index > 0) {
 308                                 *(szCur++) = _T(';');
 309                                 dataSize--;
 310                         }
 311                         if (ppPaths[index]) {
 312                                 Py_ssize_t len = _tcslen(ppPaths[index]);
 313                                 _tcsncpy(szCur, ppPaths[index], len);
 314                                 szCur += len;
 315                                 assert(dataSize > (DWORD)len);
 316                                 dataSize -= (DWORD)len;
 317                         }
 318                 }
 319                 if (skipcore)
 320                         *szCur = '\0';
 321                 else {
 322                         /* If we have no values, we dont need a ';' */
 323                         if (numKeys) {
 324                                 *(szCur++) = _T(';');
 325                                 dataSize--;
 326                         }
 327                         /* Now append the core path entries -
 328                            this will include the NULL
 329                         */
 330                         rc = RegQueryValueEx(newKey, NULL, 0, NULL,
 331                                              (LPBYTE)szCur, &dataSize);
 332                 }
 333                 /* And set the result - caller must free
 334                    If MBCS, it is fine as is.  If Unicode, allocate new
 335                    buffer and convert.
 336                 */
 337 #ifdef UNICODE
 338                 retval = (char *)malloc(reqdSize+1);
 339                 if (retval)
 340                         WideCharToMultiByte(CP_ACP, 0,
 341                                         dataBuf, -1, /* source */
 342                                         retval, reqdSize+1, /* dest */
 343                                         NULL, NULL);
 344                 free(dataBuf);
 345 #else
 346                 retval = dataBuf;
 347 #endif
 348         }
 349 done:
 350         /* Loop freeing my temp buffers */
 351         if (ppPaths) {
 352                 for(index=0;index<numKeys;index++)
 353                         if (ppPaths[index]) free(ppPaths[index]);
 354                 free(ppPaths);
 355         }
 356         if (newKey)
 357                 RegCloseKey(newKey);
 358         if (keyBuf)
 359                 free(keyBuf);
 360         return retval;
 361 }
 362 #endif /* MS_WINDOWS */
 363
 364 static void
 365 get_progpath(void)
 366 {
 367         extern char *Py_GetProgramName(void);
 368         char *path = getenv("PATH");
 369         char *prog = Py_GetProgramName();
 370
 371 #ifdef MS_WINDOWS
 372         extern HANDLE PyWin_DLLhModule;
 373 #ifdef UNICODE
 374         WCHAR wprogpath[MAXPATHLEN+1];
 375         /* Windows documents that GetModuleFileName() will "truncate",
 376            but makes no mention of the null terminator.  Play it safe.
 377            PLUS Windows itself defines MAX_PATH as the same, but anyway...
 378         */
 379         wprogpath[MAXPATHLEN]=_T('\0');
 380         if (PyWin_DLLhModule &&
 381             GetModuleFileName(PyWin_DLLhModule, wprogpath, MAXPATHLEN)) {
 382                 WideCharToMultiByte(CP_ACP, 0,
 383                                     wprogpath, -1,
 384                                     dllpath, MAXPATHLEN+1,
 385                                     NULL, NULL);
 386         }
 387         wprogpath[MAXPATHLEN]=_T('\0');
 388         if (GetModuleFileName(NULL, wprogpath, MAXPATHLEN)) {
 389                 WideCharToMultiByte(CP_ACP, 0,
 390                                     wprogpath, -1,
 391                                     progpath, MAXPATHLEN+1,
 392                                     NULL, NULL);
 393                 return;
 394         }
 395 #else
 396         /* static init of progpath ensures final char remains \0 */
 397         if (PyWin_DLLhModule)
 398                 if (!GetModuleFileName(PyWin_DLLhModule, dllpath, MAXPATHLEN))
 399                         dllpath[0] = 0;
 400         if (GetModuleFileName(NULL, progpath, MAXPATHLEN))
 401                 return;
 402 #endif
 403 #endif
 404         if (prog == NULL || *prog == '\0')
 405                 prog = "python";
 406
 407         /* If there is no slash in the argv0 path, then we have to
 408          * assume python is on the user's $PATH, since there's no
 409          * other way to find a directory to start the search from.  If
 410          * $PATH isn't exported, you lose.
 411          */
 412 #ifdef ALTSEP
 413         if (strchr(prog, SEP) || strchr(prog, ALTSEP))
 414 #else
 415         if (strchr(prog, SEP))
 416 #endif
 417                 strncpy(progpath, prog, MAXPATHLEN);
 418         else if (path) {
 419                 while (1) {
 420                         char *delim = strchr(path, DELIM);
 421
 422                         if (delim) {
 423                                 size_t len = delim - path;
 424                                 /* ensure we can't overwrite buffer */
 425                                 len = min(MAXPATHLEN,len);
 426                                 strncpy(progpath, path, len);
 427                                 *(progpath + len) = '\0';
 428                         }
 429                         else
 430                                 strncpy(progpath, path, MAXPATHLEN);
 431
 432                         /* join() is safe for MAXPATHLEN+1 size buffer */
 433                         join(progpath, prog);
 434                         if (exists(progpath))
 435                                 break;
 436
 437                         if (!delim) {
 438                                 progpath[0] = '\0';
 439                                 break;
 440                         }
 441                         path = delim + 1;
 442                 }
 443         }
 444         else
 445                 progpath[0] = '\0';
 446 }
 447
 448 static void
 449 calculate_path(void)
 450 {
 451         char argv0_path[MAXPATHLEN+1];
 452         char *buf;
 453         size_t bufsz;
 454         char *pythonhome = Py_GetPythonHome();
 455         char *envpath = Py_GETENV("PYTHONPATH");
 456
 457 #ifdef MS_WINDOWS
 458         int skiphome, skipdefault;
 459         char *machinepath = NULL;
 460         char *userpath = NULL;
 461         char zip_path[MAXPATHLEN+1];
 462         size_t len;
 463 #endif
 464
 465         get_progpath();
 466         /* progpath guaranteed \0 terminated in MAXPATH+1 bytes. */
 467         strcpy(argv0_path, progpath);
 468         reduce(argv0_path);
 469         if (pythonhome == NULL || *pythonhome == '\0') {
 470                 if (search_for_prefix(argv0_path, LANDMARK))
 471                         pythonhome = prefix;
 472                 else
 473                         pythonhome = NULL;
 474         }
 475         else
 476                 strncpy(prefix, pythonhome, MAXPATHLEN);
 477
 478         if (envpath && *envpath == '\0')
 479                 envpath = NULL;
 480
 481
 482 #ifdef MS_WINDOWS
 483         /* Calculate zip archive path */
 484         if (dllpath[0])         /* use name of python DLL */
 485                 strncpy(zip_path, dllpath, MAXPATHLEN);
 486         else                    /* use name of executable program */
 487                 strncpy(zip_path, progpath, MAXPATHLEN);
 488         zip_path[MAXPATHLEN] = '\0';
 489         len = strlen(zip_path);
 490         if (len > 4) {
 491                 zip_path[len-3] = 'z';  /* change ending to "zip" */
 492                 zip_path[len-2] = 'i';
 493                 zip_path[len-1] = 'p';
 494         }
 495         else {
 496                 zip_path[0] = 0;
 497         }
 498
 499         skiphome = pythonhome==NULL ? 0 : 1;
 500         machinepath = getpythonregpath(HKEY_LOCAL_MACHINE, skiphome);
 501         userpath = getpythonregpath(HKEY_CURRENT_USER, skiphome);
 502         /* We only use the default relative PYTHONPATH if we havent
 503            anything better to use! */
 504         skipdefault = envpath!=NULL || pythonhome!=NULL || \
 505                       machinepath!=NULL || userpath!=NULL;
 506 #endif
 507
 508         /* We need to construct a path from the following parts.
 509            (1) the PYTHONPATH environment variable, if set;
 510            (2) for Win32, the zip archive file path;
 511            (3) for Win32, the machinepath and userpath, if set;
 512            (4) the PYTHONPATH config macro, with the leading "."
 513                of each component replaced with pythonhome, if set;
 514            (5) the directory containing the executable (argv0_path).
 515            The length calculation calculates #4 first.
 516            Extra rules:
 517            - If PYTHONHOME is set (in any way) item (3) is ignored.
 518            - If registry values are used, (4) and (5) are ignored.
 519         */
 520
 521         /* Calculate size of return buffer */
 522         if (pythonhome != NULL) {
 523                 char *p;
 524                 bufsz = 1;
 525                 for (p = PYTHONPATH; *p; p++) {
 526                         if (*p == DELIM)
 527                                 bufsz++; /* number of DELIM plus one */
 528                 }
 529                 bufsz *= strlen(pythonhome);
 530         }
 531         else
 532                 bufsz = 0;
 533         bufsz += strlen(PYTHONPATH) + 1;
 534         bufsz += strlen(argv0_path) + 1;
 535 #ifdef MS_WINDOWS
 536         if (userpath)
 537                 bufsz += strlen(userpath) + 1;
 538         if (machinepath)
 539                 bufsz += strlen(machinepath) + 1;
 540         bufsz += strlen(zip_path) + 1;
 541 #endif
 542         if (envpath != NULL)
 543                 bufsz += strlen(envpath) + 1;
 544
 545         module_search_path = buf = malloc(bufsz);
 546         if (buf == NULL) {
 547                 /* We can't exit, so print a warning and limp along */
 548                 fprintf(stderr, "Can't malloc dynamic PYTHONPATH.\n");
 549                 if (envpath) {
 550                         fprintf(stderr, "Using environment $PYTHONPATH.\n");
 551                         module_search_path = envpath;
 552                 }
 553                 else {
 554                         fprintf(stderr, "Using default static path.\n");
 555                         module_search_path = PYTHONPATH;
 556                 }
 557 #ifdef MS_WINDOWS
 558                 if (machinepath)
 559                         free(machinepath);
 560                 if (userpath)
 561                         free(userpath);
 562 #endif /* MS_WINDOWS */
 563                 return;
 564         }
 565
 566         if (envpath) {
 567                 strcpy(buf, envpath);
 568                 buf = strchr(buf, '\0');
 569                 *buf++ = DELIM;
 570         }
 571 #ifdef MS_WINDOWS
 572         if (zip_path[0]) {
 573                 strcpy(buf, zip_path);
 574                 buf = strchr(buf, '\0');
 575                 *buf++ = DELIM;
 576         }
 577         if (userpath) {
 578                 strcpy(buf, userpath);
 579                 buf = strchr(buf, '\0');
 580                 *buf++ = DELIM;
 581                 free(userpath);
 582         }
 583         if (machinepath) {
 584                 strcpy(buf, machinepath);
 585                 buf = strchr(buf, '\0');
 586                 *buf++ = DELIM;
 587                 free(machinepath);
 588         }
 589         if (pythonhome == NULL) {
 590                 if (!skipdefault) {
 591                         strcpy(buf, PYTHONPATH);
 592                         buf = strchr(buf, '\0');
 593                 }
 594         }
 595 #else
 596         if (pythonhome == NULL) {
 597                 strcpy(buf, PYTHONPATH);
 598                 buf = strchr(buf, '\0');
 599         }
 600 #endif /* MS_WINDOWS */
 601         else {
 602                 char *p = PYTHONPATH;
 603                 char *q;
 604                 size_t n;
 605                 for (;;) {
 606                         q = strchr(p, DELIM);
 607                         if (q == NULL)
 608                                 n = strlen(p);
 609                         else
 610                                 n = q-p;
 611                         if (p[0] == '.' && is_sep(p[1])) {
 612                                 strcpy(buf, pythonhome);
 613                                 buf = strchr(buf, '\0');
 614                                 p++;
 615                                 n--;
 616                         }
 617                         strncpy(buf, p, n);
 618                         buf += n;
 619                         if (q == NULL)
 620                                 break;
 621                         *buf++ = DELIM;
 622                         p = q+1;
 623                 }
 624         }
 625         if (argv0_path) {
 626                 *buf++ = DELIM;
 627                 strcpy(buf, argv0_path);
 628                 buf = strchr(buf, '\0');
 629         }
 630         *buf = '\0';
 631         /* Now to pull one last hack/trick.  If sys.prefix is
 632            empty, then try and find it somewhere on the paths
 633            we calculated.  We scan backwards, as our general policy
 634            is that Python core directories are at the *end* of
 635            sys.path.  We assume that our "lib" directory is
 636            on the path, and that our 'prefix' directory is
 637            the parent of that.
 638         */
 639         if (*prefix=='\0') {
 640                 char lookBuf[MAXPATHLEN+1];
 641                 char *look = buf - 1; /* 'buf' is at the end of the buffer */
 642                 while (1) {
 643                         Py_ssize_t nchars;
 644                         char *lookEnd = look;
 645                         /* 'look' will end up one character before the
 646                            start of the path in question - even if this
 647                            is one character before the start of the buffer
 648                         */
 649                         while (*look != DELIM && look >= module_search_path)
 650                                 look--;
 651                         nchars = lookEnd-look;
 652                         strncpy(lookBuf, look+1, nchars);
 653                         lookBuf[nchars] = '\0';
 654                         /* Up one level to the parent */
 655                         reduce(lookBuf);
 656                         if (search_for_prefix(lookBuf, LANDMARK)) {
 657                                 break;
 658                         }
 659                         /* If we are out of paths to search - give up */
 660                         if (look < module_search_path)
 661                                 break;
 662                         look--;
 663                 }
 664         }
 665 }
 666
 667
 668 /* External interface */
 669
 670 char *
 671 Py_GetPath(void)
 672 {
 673         if (!module_search_path)
 674                 calculate_path();
 675         return module_search_path;
 676 }
 677
 678 char *
 679 Py_GetPrefix(void)
 680 {
 681         if (!module_search_path)
 682                 calculate_path();
 683         return prefix;
 684 }
 685
 686 char *
 687 Py_GetExecPrefix(void)
 688 {
 689         return Py_GetPrefix();
 690 }
 691
 692 char *
 693 Py_GetProgramFullPath(void)
 694 {
 695         if (!module_search_path)
 696                 calculate_path();
 697         return progpath;
 698 }