python/cpython · error

cannot open '%s' for reading

Error message

cannot open '%s' for reading

What it means

Build-time error from Programs/_freeze_module.c, the helper that freezes stdlib source into marshalled code objects during CPython builds. read_text() failed to fopen() the input .py path in 'rb' mode — the file does not exist or is unreadable — so the freeze step aborts for that module.

Source

Thrown at Programs/_freeze_module.c:90

    PyInitConfig_Free(config);
    return;

error:
    {
        const char *err_msg;
        (void)PyInitConfig_GetError(config, &err_msg);
        printf("Python init error: %s\n", err_msg);
        PyInitConfig_Free(config);
        exit(1);
    }
}

static const char *
read_text(const char *inpath)
{
    FILE *infile = fopen(inpath, "rb");
    if (infile == NULL) {
        fprintf(stderr, "cannot open '%s' for reading\n", inpath);
        return NULL;
    }

    struct _Py_stat_struct stat;
    if (_Py_fstat_noraise(fileno(infile), &stat)) {
        fprintf(stderr, "cannot fstat '%s'\n", inpath);
        fclose(infile);
        return NULL;
    }
    size_t text_size = (size_t)stat.st_size;

    char *text = (char *) malloc(text_size + 1);
    if (text == NULL) {
        fprintf(stderr, "could not allocate %ld bytes\n", (long) text_size);
        fclose(infile);
        return NULL;
    }
    size_t n = fread(text, 1, text_size, infile);

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Verify the input path exists and is readable: `ls -l <inpath>` and rerun
2. Fix the checkout: `git status` / re-clone or `git checkout -- Lib/` to restore missing files
3. If adding a new frozen module, ensure the source file path in Makefile/build lists matches the real file
4. When invoking manually, use the documented order: _freeze_module <name> <inpath> <outpath>

# shell, before building or running the freezer
# [ -r "Lib/os.py" ] || { echo 'missing input'; git checkout -- Lib; exit 1; }
# ./_freeze_module_os.sh  # only after inputs exist

When it happens

Trigger: Running `_freeze_module name in.py out.c` where in.py does not exist, has wrong permissions, or the path is wrong; in-tree when the build system references a Lib/ file that was deleted, renamed, or not checked out (shallow/sparse clone, interrupted checkout).

Common situations: Building CPython from a dirty or partial checkout; a new frozen module added to the build lists without its source file being committed; out-of-tree builds with wrong relative paths; running _freeze_module manually with misordered arguments.

Related errors

• cannot fstat '%s'
• could not allocate %ld bytes
• read too short: got %ld instead of %ld bytes
• cannot open '%s' for writing
• memory error: could not allocate varname

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/60663698dadb5a24. Report an issue: GitHub.