summaryrefslogtreecommitdiff
path: root/PC/getpathp.c
blob: b5bf325f469f3354adacf4c0366aa9a785641777 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825

/* Return the initial module search path. */
/* Used by DOS, OS/2, Windows 3.1, Windows 95/98, Windows NT. */

/* ----------------------------------------------------------------
   PATH RULES FOR WINDOWS:
   This describes how sys.path is formed on Windows.  It describes the
   functionality, not the implementation (ie, the order in which these
   are actually fetched is different)

   * Python always adds an empty entry at the start, which corresponds
     to the current directory.

   * If the PYTHONPATH env. var. exists, its entries are added next.

   * We look in the registry for "application paths" - that is, sub-keys
     under the main PythonPath registry key.  These are added next (the
     order of sub-key processing is undefined).
     HKEY_CURRENT_USER is searched and added first.
     HKEY_LOCAL_MACHINE is searched and added next.
     (Note that all known installers only use HKLM, so HKCU is typically
     empty)

   * We attempt to locate the "Python Home" - if the PYTHONHOME env var
     is set, we believe it.  Otherwise, we use the path of our host .EXE's
     to try and locate our "landmark" (lib\\os.py) and deduce our home.
     - If we DO have a Python Home: The relevant sub-directories (Lib,
       plat-win, etc) are based on the Python Home
     - If we DO NOT have a Python Home, the core Python Path is
       loaded from the registry.  This is the main PythonPath key,
       and both HKLM and HKCU are combined to form the path)

   * Iff - we can not locate the Python Home, have not had a PYTHONPATH
     specified, and can't locate any Registry entries (ie, we have _nothing_
     we can assume is a good path), a default path with relative entries is
     used (eg. .\Lib;.\plat-win, etc)


  The end result of all this is:
  * When running python.exe, or any other .exe in the main Python directory
    (either an installed version, or directly from the PCbuild directory),
    the core path is deduced, and the core paths in the registry are
    ignored.  Other "application paths" in the registry are always read.

  * When Python is hosted in another exe (different directory, embedded via
    COM, etc), the Python Home will not be deduced, so the core path from
    the registry is used.  Other "application paths" in the registry are
    always read.

  * If Python can't find its home and there is no registry (eg, frozen
    exe, some very strange installation setup) you get a path with
    some default, but relative, paths.

  * An embedding application can use Py_SetPath() to override all of
    these authomatic path computations.

   ---------------------------------------------------------------- */


#include "Python.h"
#include "osdefs.h"
#include <wchar.h>

#ifdef MS_WINDOWS
#include <windows.h>
#endif

#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif /* HAVE_SYS_TYPES_H */

#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif /* HAVE_SYS_STAT_H */

#include <string.h>

/* Search in some common locations for the associated Python libraries.
 *
 * Py_GetPath() tries to return a sensible Python module search path.
 *
 * The approach is an adaptation for Windows of the strategy used in
 * ../Modules/getpath.c; it uses the Windows Registry as one of its
 * information sources.
 *
 * Py_SetPath() can be used to override this mechanism.  Call Py_SetPath
 * with a semicolon separated path prior to calling Py_Initialize.
 */

#ifndef LANDMARK
#define LANDMARK L"lib\\os.py"
#endif

static wchar_t prefix[MAXPATHLEN+1];
static wchar_t progpath[MAXPATHLEN+1];
static wchar_t dllpath[MAXPATHLEN+1];
static wchar_t *module_search_path = NULL;


static int
is_sep(wchar_t ch)      /* determine if "ch" is a separator character */
{
#ifdef ALTSEP
    return ch == SEP || ch == ALTSEP;
#else
    return ch == SEP;
#endif
}

/* assumes 'dir' null terminated in bounds.  Never writes
   beyond existing terminator.
*/
static void
reduce(wchar_t *dir)
{
    size_t i = wcslen(dir);
    while (i > 0 && !is_sep(dir[i]))
        --i;
    dir[i] = '\0';
}


static int
exists(wchar_t *filename)
{
    return GetFileAttributesW(filename) != 0xFFFFFFFF;
}

/* Assumes 'filename' MAXPATHLEN+1 bytes long -
   may extend 'filename' by one character.
*/
static int
ismodule(wchar_t *filename)     /* Is module -- check for .pyc/.pyo too */
{
    if (exists(filename))
        return 1;

    /* Check for the compiled version of prefix. */
    if (wcslen(filename) < MAXPATHLEN) {
        wcscat(filename, Py_OptimizeFlag ? L"o" : L"c");
        if (exists(filename))
            return 1;
    }
    return 0;
}

/* Add a path component, by appending stuff to buffer.
   buffer must have at least MAXPATHLEN + 1 bytes allocated, and contain a
   NUL-terminated string with no more than MAXPATHLEN characters (not counting
   the trailing NUL).  It's a fatal error if it contains a string longer than
   that (callers must be careful!).  If these requirements are met, it's
   guaranteed that buffer will still be a NUL-terminated string with no more
   than MAXPATHLEN characters at exit.  If stuff is too long, only as much of
   stuff as fits will be appended.
*/
static void
join(wchar_t *buffer, wchar_t *stuff)
{
    size_t n, k;
    if (is_sep(stuff[0]))
        n = 0;
    else {
        n = wcslen(buffer);
        if (n > 0 && !is_sep(buffer[n-1]) && n < MAXPATHLEN)
            buffer[n++] = SEP;
    }
    if (n > MAXPATHLEN)
        Py_FatalError("buffer overflow in getpathp.c's joinpath()");
    k = wcslen(stuff);
    if (n + k > MAXPATHLEN)
        k = MAXPATHLEN - n;
    wcsncpy(buffer+n, stuff, k);
    buffer[n+k] = '\0';
}

/* gotlandmark only called by search_for_prefix, which ensures
   'prefix' is null terminated in bounds.  join() ensures
   'landmark' can not overflow prefix if too long.
*/
static int
gotlandmark(wchar_t *landmark)
{
    int ok;
    Py_ssize_t n;

    n = wcslen(prefix);
    join(prefix, landmark);
    ok = ismodule(prefix);
    prefix[n] = '\0';
    return ok;
}

/* assumes argv0_path is MAXPATHLEN+1 bytes long, already \0 term'd.
   assumption provided by only caller, calculate_path() */
static int
search_for_prefix(wchar_t *argv0_path, wchar_t *landmark)
{
    /* Search from argv0_path, until landmark is found */
    wcscpy(prefix, argv0_path);
    do {
        if (gotlandmark(landmark))
            return 1;
        reduce(prefix);
    } while (prefix[0]);
    return 0;
}

#ifdef MS_WINDOWS
#ifdef Py_ENABLE_SHARED

/* a string loaded from the DLL at startup.*/
extern const char *PyWin_DLLVersionString;


/* Load a PYTHONPATH value from the registry.
   Load from either HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER.

   Works in both Unicode and 8bit environments.  Only uses the
   Ex family of functions so it also works with Windows CE.

   Returns NULL, or a pointer that should be freed.

   XXX - this code is pretty strange, as it used to also
   work on Win16, where the buffer sizes werent available
   in advance.  It could be simplied now Win16/Win32s is dead!
*/

static wchar_t *
getpythonregpath(HKEY keyBase, int skipcore)
{
    HKEY newKey = 0;
    DWORD dataSize = 0;
    DWORD numKeys = 0;
    LONG rc;
    wchar_t *retval = NULL;
    WCHAR *dataBuf = NULL;
    static const WCHAR keyPrefix[] = L"Software\\Python\\PythonCore\\";
    static const WCHAR keySuffix[] = L"\\PythonPath";
    size_t versionLen;
    DWORD index;
    WCHAR *keyBuf = NULL;
    WCHAR *keyBufPtr;
    WCHAR **ppPaths = NULL;

    /* Tried to use sysget("winver") but here is too early :-( */
    versionLen = strlen(PyWin_DLLVersionString);
    /* Space for all the chars, plus one \0 */
    keyBuf = keyBufPtr = malloc(sizeof(keyPrefix) +
                                sizeof(WCHAR)*(versionLen-1) +
                                sizeof(keySuffix));
    if (keyBuf==NULL) goto done;

    memcpy(keyBufPtr, keyPrefix, sizeof(keyPrefix)-sizeof(WCHAR));
    keyBufPtr += Py_ARRAY_LENGTH(keyPrefix) - 1;
    mbstowcs(keyBufPtr, PyWin_DLLVersionString, versionLen);
    keyBufPtr += versionLen;
    /* NULL comes with this one! */
    memcpy(keyBufPtr, keySuffix, sizeof(keySuffix));
    /* Open the root Python key */
    rc=RegOpenKeyExW(keyBase,
                    keyBuf, /* subkey */
            0, /* reserved */
            KEY_READ,
            &newKey);
    if (rc!=ERROR_SUCCESS) goto done;
    /* Find out how big our core buffer is, and how many subkeys we have */
    rc = RegQueryInfoKey(newKey, NULL, NULL, NULL, &numKeys, NULL, NULL,
                    NULL, NULL, &dataSize, NULL, NULL);
    if (rc!=ERROR_SUCCESS) goto done;
    if (skipcore) dataSize = 0; /* Only count core ones if we want them! */
    /* Allocate a temp array of char buffers, so we only need to loop
       reading the registry once
    */
    ppPaths = malloc( sizeof(WCHAR *) * numKeys );
    if (ppPaths==NULL) goto done;
    memset(ppPaths, 0, sizeof(WCHAR *) * numKeys);
    /* Loop over all subkeys, allocating a temp sub-buffer. */
    for(index=0;index<numKeys;index++) {
        WCHAR keyBuf[MAX_PATH+1];
        HKEY subKey = 0;
        DWORD reqdSize = MAX_PATH+1;
        /* Get the sub-key name */
        DWORD rc = RegEnumKeyExW(newKey, index, keyBuf, &reqdSize,
                                 NULL, NULL, NULL, NULL );
        if (rc!=ERROR_SUCCESS) goto done;
        /* Open the sub-key */
        rc=RegOpenKeyExW(newKey,
                                        keyBuf, /* subkey */
                        0, /* reserved */
                        KEY_READ,
                        &subKey);
        if (rc!=ERROR_SUCCESS) goto done;
        /* Find the value of the buffer size, malloc, then read it */
        RegQueryValueExW(subKey, NULL, 0, NULL, NULL, &reqdSize);
        if (reqdSize) {
            ppPaths[index] = malloc(reqdSize);
            if (ppPaths[index]) {
                RegQueryValueExW(subKey, NULL, 0, NULL,
                                (LPBYTE)ppPaths[index],
                                &reqdSize);
                dataSize += reqdSize + 1; /* 1 for the ";" */
            }
        }
        RegCloseKey(subKey);
    }

    /* return null if no path to return */
    if (dataSize == 0) goto done;

    /* original datasize from RegQueryInfo doesn't include the \0 */
    dataBuf = malloc((dataSize+1) * sizeof(WCHAR));
    if (dataBuf) {
        WCHAR *szCur = dataBuf;
        DWORD reqdSize = dataSize;
        /* Copy our collected strings */
        for (index=0;index<numKeys;index++) {
            if (index > 0) {
                *(szCur++) = L';';
                dataSize--;
            }
            if (ppPaths[index]) {
                Py_ssize_t len = wcslen(ppPaths[index]);
                wcsncpy(szCur, ppPaths[index], len);
                szCur += len;
                assert(dataSize > (DWORD)len);
                dataSize -= (DWORD)len;
            }
        }
        if (skipcore)
            *szCur = '\0';
        else {
            /* If we have no values, we dont need a ';' */
            if (numKeys) {
                *(szCur++) = L';';
                dataSize--;
            }
            /* Now append the core path entries -
               this will include the NULL
            */
            rc = RegQueryValueExW(newKey, NULL, 0, NULL,
                                  (LPBYTE)szCur, &dataSize);
        }
        /* And set the result - caller must free */
        retval = dataBuf;
    }
done:
    /* Loop freeing my temp buffers */
    if (ppPaths) {
        for(index=0;index<numKeys;index++)
            if (ppPaths[index]) free(ppPaths[index]);
        free(ppPaths);
    }
    if (newKey)
        RegCloseKey(newKey);
    if (keyBuf)
        free(keyBuf);
    return retval;
}
#endif /* Py_ENABLE_SHARED */
#endif /* MS_WINDOWS */

static void
get_progpath(void)
{
    extern wchar_t *Py_GetProgramName(void);
    wchar_t *path = _wgetenv(L"PATH");
    wchar_t *prog = Py_GetProgramName();

#ifdef MS_WINDOWS
#ifdef Py_ENABLE_SHARED
    extern HANDLE PyWin_DLLhModule;
    /* static init of progpath ensures final char remains \0 */
    if (PyWin_DLLhModule)
        if (!GetModuleFileNameW(PyWin_DLLhModule, dllpath, MAXPATHLEN))
            dllpath[0] = 0;
#else
    dllpath[0] = 0;
#endif
    if (GetModuleFileNameW(NULL, progpath, MAXPATHLEN))
        return;
#endif
    if (prog == NULL || *prog == '\0')
        prog = L"python";

    /* If there is no slash in the argv0 path, then we have to
     * assume python is on the user's $PATH, since there's no
     * other way to find a directory to start the search from.  If
     * $PATH isn't exported, you lose.
     */
#ifdef ALTSEP
    if (wcschr(prog, SEP) || wcschr(prog, ALTSEP))
#else
    if (wcschr(prog, SEP))
#endif
        wcsncpy(progpath, prog, MAXPATHLEN);
    else if (path) {
        while (1) {
            wchar_t *delim = wcschr(path, DELIM);

            if (delim) {
                size_t len = delim - path;
                /* ensure we can't overwrite buffer */
                len = min(MAXPATHLEN,len);
                wcsncpy(progpath, path, len);
                *(progpath + len) = '\0';
            }
            else
                wcsncpy(progpath, path, MAXPATHLEN);

            /* join() is safe for MAXPATHLEN+1 size buffer */
            join(progpath, prog);
            if (exists(progpath))
                break;

            if (!delim) {
                progpath[0] = '\0';
                break;
            }
            path = delim + 1;
        }
    }
    else
        progpath[0] = '\0';
}

static int
find_env_config_value(FILE * env_file, const wchar_t * key, wchar_t * value)
{
    int result = 0; /* meaning not found */
    char buffer[MAXPATHLEN*2+1];  /* allow extra for key, '=', etc. */

    fseek(env_file, 0, SEEK_SET);
    while (!feof(env_file)) {
        char * p = fgets(buffer, MAXPATHLEN*2, env_file);
        wchar_t tmpbuffer[MAXPATHLEN*2+1];
        PyObject * decoded;
        int n;

        if (p == NULL)
            break;
        n = strlen(p);
        if (p[n - 1] != '\n') {
            /* line has overflowed - bail */
            break;
        }
        if (p[0] == '#')    /* Comment - skip */
            continue;
        decoded = PyUnicode_DecodeUTF8(buffer, n, "surrogateescape");
        if (decoded != NULL) {
            Py_ssize_t k;
            k = PyUnicode_AsWideChar(decoded,
                                     tmpbuffer, MAXPATHLEN * 2);
            Py_DECREF(decoded);
            if (k >= 0) {
                wchar_t * tok = wcstok(tmpbuffer, L" \t\r\n");
                if ((tok != NULL) && !wcscmp(tok, key)) {
                    tok = wcstok(NULL, L" \t");
                    if ((tok != NULL) && !wcscmp(tok, L"=")) {
                        tok = wcstok(NULL, L"\r\n");
                        if (tok != NULL) {
                            wcsncpy(value, tok, MAXPATHLEN);
                            result = 1;
                            break;
                        }
                    }
                }
            }
        }
    }
    return result;
}

static void
calculate_path(void)
{
    wchar_t argv0_path[MAXPATHLEN+1];
    wchar_t *buf;
    size_t bufsz;
    wchar_t *pythonhome = Py_GetPythonHome();
    wchar_t *envpath = NULL;

#ifdef MS_WINDOWS
    int skiphome, skipdefault;
    wchar_t *machinepath = NULL;
    wchar_t *userpath = NULL;
    wchar_t zip_path[MAXPATHLEN+1];
    size_t len;

    if (!Py_IgnoreEnvironmentFlag) {
        envpath = _wgetenv(L"PYTHONPATH");
    }
#else
    char *_envpath = Py_GETENV("PYTHONPATH");
    wchar_t wenvpath[MAXPATHLEN+1];
    if (_envpath) {
        size_t r = mbstowcs(wenvpath, _envpath, MAXPATHLEN+1);
        envpath = wenvpath;
        if (r == (size_t)-1 || r >= MAXPATHLEN)
            envpath = NULL;
    }
#endif

    get_progpath();
    /* progpath guaranteed \0 terminated in MAXPATH+1 bytes. */
    wcscpy(argv0_path, progpath);
    reduce(argv0_path);

    /* Search for an environment configuration file, first in the
       executable's directory and then in the parent directory.
       If found, open it for use when searching for prefixes.
    */

    {
        wchar_t tmpbuffer[MAXPATHLEN+1];
        wchar_t *env_cfg = L"pyvenv.cfg";
        FILE * env_file = NULL;

        wcscpy(tmpbuffer, argv0_path);
        join(tmpbuffer, env_cfg);
        env_file = _Py_wfopen(tmpbuffer, L"r");
        if (env_file == NULL) {
            errno = 0;
            reduce(tmpbuffer);
            reduce(tmpbuffer);
            join(tmpbuffer, env_cfg);
            env_file = _Py_wfopen(tmpbuffer, L"r");
            if (env_file == NULL) {
                errno = 0;
            }
        }
        if (env_file != NULL) {
            /* Look for a 'home' variable and set argv0_path to it, if found */
            if (find_env_config_value(env_file, L"home", tmpbuffer)) {
                wcscpy(argv0_path, tmpbuffer);
            }
            fclose(env_file);
            env_file = NULL;
        }
    }

    if (pythonhome == NULL || *pythonhome == '\0') {
        if (search_for_prefix(argv0_path, LANDMARK))
            pythonhome = prefix;
        else
            pythonhome = NULL;
    }
    else
        wcsncpy(prefix, pythonhome, MAXPATHLEN);

    if (envpath && *envpath == '\0')
        envpath = NULL;


#ifdef MS_WINDOWS
    /* Calculate zip archive path */
    if (dllpath[0])             /* use name of python DLL */
        wcsncpy(zip_path, dllpath, MAXPATHLEN);
    else                        /* use name of executable program */
        wcsncpy(zip_path, progpath, MAXPATHLEN);
    zip_path[MAXPATHLEN] = '\0';
    len = wcslen(zip_path);
    if (len > 4) {
        zip_path[len-3] = 'z';          /* change ending to "zip" */
        zip_path[len-2] = 'i';
        zip_path[len-1] = 'p';
    }
    else {
        zip_path[0] = 0;
    }

    skiphome = pythonhome==NULL ? 0 : 1;
#ifdef Py_ENABLE_SHARED
    machinepath = getpythonregpath(HKEY_LOCAL_MACHINE, skiphome);
    userpath = getpythonregpath(HKEY_CURRENT_USER, skiphome);
#endif
    /* We only use the default relative PYTHONPATH if we havent
       anything better to use! */
    skipdefault = envpath!=NULL || pythonhome!=NULL || \
                  machinepath!=NULL || userpath!=NULL;
#endif

    /* We need to construct a path from the following parts.
       (1) the PYTHONPATH environment variable, if set;
       (2) for Win32, the zip archive file path;
       (3) for Win32, the machinepath and userpath, if set;
       (4) the PYTHONPATH config macro, with the leading "."
           of each component replaced with pythonhome, if set;
       (5) the directory containing the executable (argv0_path).
       The length calculation calculates #4 first.
       Extra rules:
       - If PYTHONHOME is set (in any way) item (3) is ignored.
       - If registry values are used, (4) and (5) are ignored.
    */

    /* Calculate size of return buffer */
    if (pythonhome != NULL) {
        wchar_t *p;
        bufsz = 1;
        for (p = PYTHONPATH; *p; p++) {
            if (*p == DELIM)
                bufsz++; /* number of DELIM plus one */
        }
        bufsz *= wcslen(pythonhome);
    }
    else
        bufsz = 0;
    bufsz += wcslen(PYTHONPATH) + 1;
    bufsz += wcslen(argv0_path) + 1;
#ifdef MS_WINDOWS
    if (userpath)
        bufsz += wcslen(userpath) + 1;
    if (machinepath)
        bufsz += wcslen(machinepath) + 1;
    bufsz += wcslen(zip_path) + 1;
#endif
    if (envpath != NULL)
        bufsz += wcslen(envpath) + 1;

    module_search_path = buf = malloc(bufsz*sizeof(wchar_t));
    if (buf == NULL) {
        /* We can't exit, so print a warning and limp along */
        fprintf(stderr, "Can't malloc dynamic PYTHONPATH.\n");
        if (envpath) {
            fprintf(stderr, "Using environment $PYTHONPATH.\n");
            module_search_path = envpath;
        }
        else {
            fprintf(stderr, "Using default static path.\n");
            module_search_path = PYTHONPATH;
        }
#ifdef MS_WINDOWS
        if (machinepath)
            free(machinepath);
        if (userpath)
            free(userpath);
#endif /* MS_WINDOWS */
        return;
    }

    if (envpath) {
        wcscpy(buf, envpath);
        buf = wcschr(buf, L'\0');
        *buf++ = DELIM;
    }
#ifdef MS_WINDOWS
    if (zip_path[0]) {
        wcscpy(buf, zip_path);
        buf = wcschr(buf, L'\0');
        *buf++ = DELIM;
    }
    if (userpath) {
        wcscpy(buf, userpath);
        buf = wcschr(buf, L'\0');
        *buf++ = DELIM;
        free(userpath);
    }
    if (machinepath) {
        wcscpy(buf, machinepath);
        buf = wcschr(buf, L'\0');
        *buf++ = DELIM;
        free(machinepath);
    }
    if (pythonhome == NULL) {
        if (!skipdefault) {
            wcscpy(buf, PYTHONPATH);
            buf = wcschr(buf, L'\0');
        }
    }
#else
    if (pythonhome == NULL) {
        wcscpy(buf, PYTHONPATH);
        buf = wcschr(buf, L'\0');
    }
#endif /* MS_WINDOWS */
    else {
        wchar_t *p = PYTHONPATH;
        wchar_t *q;
        size_t n;
        for (;;) {
            q = wcschr(p, DELIM);
            if (q == NULL)
                n = wcslen(p);
            else
                n = q-p;
            if (p[0] == '.' && is_sep(p[1])) {
                wcscpy(buf, pythonhome);
                buf = wcschr(buf, L'\0');
                p++;
                n--;
            }
            wcsncpy(buf, p, n);
            buf += n;
            if (q == NULL)
                break;
            *buf++ = DELIM;
            p = q+1;
        }
    }
    if (argv0_path) {
        *buf++ = DELIM;
        wcscpy(buf, argv0_path);
        buf = wcschr(buf, L'\0');
    }
    *buf = L'\0';
    /* Now to pull one last hack/trick.  If sys.prefix is
       empty, then try and find it somewhere on the paths
       we calculated.  We scan backwards, as our general policy
       is that Python core directories are at the *end* of
       sys.path.  We assume that our "lib" directory is
       on the path, and that our 'prefix' directory is
       the parent of that.
    */
    if (*prefix==L'\0') {
        wchar_t lookBuf[MAXPATHLEN+1];
        wchar_t *look = buf - 1; /* 'buf' is at the end of the buffer */
        while (1) {
            Py_ssize_t nchars;
            wchar_t *lookEnd = look;
            /* 'look' will end up one character before the
               start of the path in question - even if this
               is one character before the start of the buffer
            */
            while (look >= module_search_path && *look != DELIM)
                look--;
            nchars = lookEnd-look;
            wcsncpy(lookBuf, look+1, nchars);
            lookBuf[nchars] = L'\0';
            /* Up one level to the parent */
            reduce(lookBuf);
            if (search_for_prefix(lookBuf, LANDMARK)) {
                break;
            }
            /* If we are out of paths to search - give up */
            if (look < module_search_path)
                break;
            look--;
        }
    }
}


/* External interface */

void
Py_SetPath(const wchar_t *path)
{
    if (module_search_path != NULL) {
        free(module_search_path);
        module_search_path = NULL;
    }
    if (path != NULL) {
        extern wchar_t *Py_GetProgramName(void);
        wchar_t *prog = Py_GetProgramName();
        wcsncpy(progpath, prog, MAXPATHLEN);
        prefix[0] = L'\0';
        module_search_path = malloc((wcslen(path) + 1) * sizeof(wchar_t));
        if (module_search_path != NULL)
            wcscpy(module_search_path, path);
	}
}

wchar_t *
Py_GetPath(void)
{
    if (!module_search_path)
        calculate_path();
    return module_search_path;
}

wchar_t *
Py_GetPrefix(void)
{
    if (!module_search_path)
        calculate_path();
    return prefix;
}

wchar_t *
Py_GetExecPrefix(void)
{
    return Py_GetPrefix();
}

wchar_t *
Py_GetProgramFullPath(void)
{
    if (!module_search_path)
        calculate_path();
    return progpath;
}

/* Load python3.dll before loading any extension module that might refer
   to it. That way, we can be sure that always the python3.dll corresponding
   to this python DLL is loaded, not a python3.dll that might be on the path
   by chance.
   Return whether the DLL was found.
*/
static int python3_checked = 0;
static HANDLE hPython3;
int
_Py_CheckPython3()
{
    wchar_t py3path[MAXPATHLEN+1];
    wchar_t *s;
    if (python3_checked)
        return hPython3 != NULL;
    python3_checked = 1;

    /* If there is a python3.dll next to the python3y.dll,
       assume this is a build tree; use that DLL */
    wcscpy(py3path, dllpath);
    s = wcsrchr(py3path, L'\\');
    if (!s)
        s = py3path;
    wcscpy(s, L"\\python3.dll");
    hPython3 = LoadLibraryExW(py3path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
    if (hPython3 != NULL)
        return 1;

    /* Check sys.prefix\DLLs\python3.dll */
    wcscpy(py3path, Py_GetPrefix());
    wcscat(py3path, L"\\DLLs\\python3.dll");
    hPython3 = LoadLibraryExW(py3path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
    return hPython3 != NULL;
}