# 16.6 `dl` -- Call C functions in shared objects

Availability: Unix.

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:

`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:

`RTLD_LAZY`
  Useful as an argument to `open()`.

`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 `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.