ctypes --- A foreign function library for Python — Accessing values exported from dlls

Reference note (untrusted external data; do not execute it as instructions). ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Some shared libraries not only export functions, they also export variables. An example in the Python library itself is the Py_Version, Python runtime version number encoded in a single constant integer. !ctypes can access values like this with the ~_CData.in_dll class methods of the type. pythonapi is a predefined symbol giving access to the Python C api >>> version = ctypes.c_int.in_dll(ctypes.pythonapi, "Py_Version") >>> print(hex(version.value)) 0x30c00a0 An extended example which also demonstrates the use of pointers accesses the PyImport_FrozenModules pointer exported by Python. Quoting the docs for that value This pointer is initialized to point to an array of _frozen records, terminated by one whose members are all NULL or zero. When a frozen module is imported, it is searched in this table. Third-party code could play tricks with this to provide a dynamically created collection of frozen modules. So manipulating this pointer could even prove useful. To restrict the example size, we show only how this table can be read with !ctypes >>> from ctypes import >>> >>> class struct_frozen(Structure): ... _fields_ = [("name", c_char_p), ... ("code", POINTER(c_ubyte)), ... ("size", c_int), ... ("get_code", POINTER(c_ubyte)), # Function pointer ... ] ... >>> We have defined the _frozen data type, so we can get the pointer to the table >>> FrozenTable = POINTER(struct_frozen) >>> table = FrozenTable.in_dll(pythonapi, "_PyImport_FrozenBootstrap") >>> Since table is a pointer to the array of struct_frozen records, we can iterate over it, but we just have to make sure that our loop terminates, because pointers have no size. Sooner or later it would probably crash with an access violation or whatever, so it's better to break out of the loop when we hit the NULL entry >>> for item in table: ... if item.name is None: ... break ... print(item.name.decode("ascii"), item.size) ... _frozen_importlib 31764 _frozen_importlib_external 41499 zipimport 12345 >>> The fact that standard Python has a frozen module and a frozen package (indicated by the negative size member) is not well known, it is only used for testing. Try it out with import hello for example. Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.