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ctypes.CDLL on Linux creates a "main program" object when passed an empty string #99874
Description
Bug report
ctypes.CDLL throws an exception when it can't find a library in the path pointed at by its name argument; however, if name is an empty string a dummy object is created:
>>> import ctypes
>>> ctypes.CDLL('')
<CDLL '', handle 7fb30d2d3190 at 0x7fb30c2caa60>
I don't think this is correct, since that dummy object will break things when trying to use it later on.
Your environment
- CPython versions tested on: 3.8.10, 3.10.8
- Operating system and architecture: Ubuntu 20.04.5 LTS for x86_64
This doesn't happen on Windows with Python 3.10.7; there I see an exception being thrown for the empty string.
Activity
eryksun commentedon Nov 29, 2022
_ctypes.dlopen()converts the string viaPyUnicode_FSConverter()and passes it to to the systemdlopen()function. The interpretation of an empty string depends on the system. Fordlopen(), POSIX does not specify the behavior whenfileis an empty string. On Linux, it's the same as passingNULL. For example:WinAPI
LoadLibraryExW()requires a library name to load, which cannot be an empty string orNULL.eryksun commentedon Nov 30, 2022
The documentation does contain a general statement to this effect:
However, it's not explicit about how the pathname is used with respect to the platform library loading function. On POSIX, it's just passed along to
dlopen(). On Windows, ifwinmodeisn't used, any name that includes a path separator is first resolved as an absolute path, and the loader flags value is modified to includeLOAD_LIBRARY_SEARCH_DLL_LOAD_DIR. On AIX, certain pathnames can modify themodeparameter.Note that
ctypes.pythonapiis implemented asPyDLL(None)on POSIX, which depends on the documented behavior ofdlopen(). But this fact is not explicitly mentioned in the ctypes documentation.[-]ctypes.CDLL creates a dummy object when passed an empty string[/-][+]ctypes.CDLL on Linux creates a "main program" object when passed an empty string[/+]ZeroIntensity commentedon Oct 21, 2026
I think this was done by the rewrite in #145313.