36.6. dl — Call C functions in shared objects¶
Deprecated since version 2.6: The dl module has been removed in Python 3. Use the ctypes
module instead.
The dl module defines an interface to the 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 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, SystemError will be raised on import.
The dl module defines the following function:
-
dl.open(name[, mode=RTLD_LAZY])¶
Open a shared object file, and return a handle. Mode signifies late binding
(RTLD_LAZY) or immediate binding (RTLD_NOW). Default is
RTLD_LAZY. Note that some systems do not support RTLD_NOW.
Return value is a dlobject.
The dl module defines the following constants:
-
dl.RTLD_LAZY¶
Useful as an argument to open().
-
dl.RTLD_NOW¶
Useful as an argument to open(). Note that on systems which do not
support immediate binding, this constant will not appear in the module. For
maximum portability, use hasattr() to determine if the system supports
immediate binding.
The dl module defines the following exception:
-
exception
dl.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.
36.6.1. Dl Objects¶
Dl objects, as returned by open() above, have the following methods:
-
dl.close()¶
Free all resources, except the memory.
-
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)
-
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 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 long, which is a
Python integer.