BUG: File descriptor leak in npy_PyFile_Dup2 when fdopen fails #32373

Describe the issue:

In numpy/_core/include/numpy/npy_3kcompat.h, the function npy_PyFile_Dup2 (used by numpy.fromfile and ndarray.tofile) has a file descriptor leak on an error path.

When os.dup() succeeds but the subsequent fdopen() call fails, the duplicated file descriptor fd2 is never closed. The code sets a Python error and returns NULL without calling close(fd2):

// npy_3kcompat.h, around line 113-127
#ifdef _WIN32
    NPY_BEGIN_SUPPRESS_IPH
    handle = _fdopen(fd2, mode);
    NPY_END_SUPPRESS_IPH
#else
    handle = fdopen(fd2, mode);
#endif
    if (handle == NULL) {
        PyErr_SetString(PyExc_IOError,
                        "Getting a FILE* from a Python file object via "
                        "_fdopen failed. If you built NumPy, you probably "
                        "linked with the wrong debug/release runtime");
        return NULL;  // <-- fd2 is leaked here
    }

All other error paths after fdopen succeeds properly call fclose(handle), so this is the only leak.

Reproduce the code example:

Add a platform-appropriate raw fd close before returning `NULL`:


    if (handle == NULL) {
+#ifdef _WIN32
+       _close(fd2);
+#else
+       close(fd2);
+#endif
        PyErr_SetString(PyExc_IOError,
                        "Getting a FILE* from a Python file object via "
                        "_fdopen failed. If you built NumPy, you probably "
                        "linked with the wrong debug/release runtime");
        return NULL;
    }


Note: `fclose` cannot be used here because `fdopen` failed, so there is no valid `FILE*` handle — only the raw file descriptor `fd2` needs to be cleaned up.

Error message:

Python and NumPy Versions:

2.6.0.dev0
3.14.4 (main, Apr 8 2026, 04:02:31) [GCC 15.2.0]

Runtime Environment:

No response

How does this issue affect you or how did you find it:

This issue was found by Claude Code while analyzing the fromfile implementation for potential resource handling problems.