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:mod:`dl` --- Call C functions in shared objects ================================================ .. module:: dl :platform: Unix :synopsis: Call C functions in shared objects. :deprecated: .. deprecated:: 2.6 The :mod:`dl` module has been removed in Python 3. Use the :mod:`ctypes` module instead. .. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il> The :mod:`dl` module defines an interface to the :c:func:`dlopen` function, which is the most common interface on Unix platforms for handling dynamically linked libraries. It allows the program to call arbitrary functions in such a library. .. warning:: The :mod:`dl` module bypasses the Python type system and error handling. If used incorrectly it may cause segmentation faults, crashes or other incorrect behaviour. .. note:: This module will not work unless ``sizeof(int) == sizeof(long) == sizeof(char *)`` If this is not the case, :exc:`SystemError` will be raised on import. The :mod:`dl` module defines the following function: .. function:: open(name[, mode=RTLD_LAZY]) Open a shared object file, and return a handle. Mode signifies late binding (:const:`RTLD_LAZY`) or immediate binding (:const:`RTLD_NOW`). Default is :const:`RTLD_LAZY`. Note that some systems do not support :const:`RTLD_NOW`. Return value is a :class:`dlobject`. The :mod:`dl` module defines the following constants: .. data:: RTLD_LAZY Useful as an argument to :func:`.open`. .. data:: RTLD_NOW Useful as an argument to :func:`.open`. Note that on systems which do not support immediate binding, this constant will not appear in the module. For maximum portability, use :func:`hasattr` to determine if the system supports immediate binding. The :mod:`dl` module defines the following exception: .. exception:: error Exception raised when an error has occurred inside the dynamic loading and linking routines. Example:: >>> import dl, time >>> a=dl.open('/lib/libc.so.6') >>> a.call('time'), time.time() (929723914, 929723914.498) This example was tried on a Debian GNU/Linux system, and is a good example of the fact that using this module is usually a bad alternative. .. _dl-objects: Dl Objects ---------- Dl objects, as returned by :func:`.open` above, have the following methods: .. method:: dl.close() Free all resources, except the memory. .. method:: dl.sym(name) Return the pointer for the function named *name*, as a number, if it exists in the referenced shared object, otherwise ``None``. This is useful in code like:: >>> if a.sym('time'): ... a.call('time') ... else: ... time.time() (Note that this function will return a non-zero number, as zero is the *NULL* pointer) .. method:: dl.call(name[, arg1[, arg2...]]) Call the function named *name* in the referenced shared object. The arguments must be either Python integers, which will be passed as is, Python strings, to which a pointer will be passed, or ``None``, which will be passed as *NULL*. Note that strings should only be passed to functions as :c:type:`const char\*`, as Python will not like its string mutated. There must be at most 10 arguments, and arguments not given will be treated as ``None``. The function's return value must be a C :c:type:`long`, which is a Python integer.