1
2:mod:`dl` --- Call C functions in shared objects
3================================================
4
5.. module:: dl
6   :platform: Unix
7   :synopsis: Call C functions in shared objects.
8   :deprecated:
9
10.. deprecated:: 2.6
11    The :mod:`dl` module has been removed in Python 3. Use the :mod:`ctypes`
12    module instead.
13
14.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
15
16The :mod:`dl` module defines an interface to the :c:func:`dlopen` function, which
17is the most common interface on Unix platforms for handling dynamically linked
18libraries. It allows the program to call arbitrary functions in such a library.
19
20.. warning::
21
22   The :mod:`dl` module bypasses the Python type system and  error handling. If
23   used incorrectly it may cause segmentation faults, crashes or other incorrect
24   behaviour.
25
26.. note::
27
28   This module will not work unless ``sizeof(int) == sizeof(long) == sizeof(char
29   *)`` If this is not the case, :exc:`SystemError` will be raised on import.
30
31The :mod:`dl` module defines the following function:
32
33
34.. function:: open(name[, mode=RTLD_LAZY])
35
36   Open a shared object file, and return a handle. Mode signifies late binding
37   (:const:`RTLD_LAZY`) or immediate binding (:const:`RTLD_NOW`). Default is
38   :const:`RTLD_LAZY`. Note that some systems do not support :const:`RTLD_NOW`.
39
40   Return value is a :class:`dlobject`.
41
42The :mod:`dl` module defines the following constants:
43
44
45.. data:: RTLD_LAZY
46
47   Useful as an argument to :func:`.open`.
48
49
50.. data:: RTLD_NOW
51
52   Useful as an argument to :func:`.open`.  Note that on systems which do not
53   support immediate binding, this constant will not appear in the module. For
54   maximum portability, use :func:`hasattr` to determine if the system supports
55   immediate binding.
56
57The :mod:`dl` module defines the following exception:
58
59
60.. exception:: error
61
62   Exception raised when an error has occurred inside the dynamic loading and
63   linking routines.
64
65Example::
66
67   >>> import dl, time
68   >>> a=dl.open('/lib/libc.so.6')
69   >>> a.call('time'), time.time()
70   (929723914, 929723914.498)
71
72This example was tried on a Debian GNU/Linux system, and is a good example of
73the fact that using this module is usually a bad alternative.
74
75
76.. _dl-objects:
77
78Dl Objects
79----------
80
81Dl objects, as returned by :func:`.open` above, have the following methods:
82
83
84.. method:: dl.close()
85
86   Free all resources, except the memory.
87
88
89.. method:: dl.sym(name)
90
91   Return the pointer for the function named *name*, as a number, if it exists in
92   the referenced shared object, otherwise ``None``. This is useful in code like::
93
94      >>> if a.sym('time'):
95      ...     a.call('time')
96      ... else:
97      ...     time.time()
98
99   (Note that this function will return a non-zero number, as zero is the *NULL*
100   pointer)
101
102
103.. method:: dl.call(name[, arg1[, arg2...]])
104
105   Call the function named *name* in the referenced shared object. The arguments
106   must be either Python integers, which will be  passed as is, Python strings, to
107   which a pointer will be passed,  or ``None``, which will be passed as *NULL*.
108   Note that  strings should only be passed to functions as :c:type:`const char\*`,
109   as Python will not like its string mutated.
110
111   There must be at most 10 arguments, and arguments not given will be treated as
112   ``None``. The function's return value must be a C :c:type:`long`, which is a
113   Python integer.
114
115