wiki:Features/CtypesDependencySupport

Ctypes dependency support

Ctypes is a foreign function library for Python, that allows calling functions present in shared libraries. Those libraries are not imported as Python packages, because they are not picked up via Python imports: their path is passed to ctypes instead, which deals with the shared library directly; this caused <1.4 PyInstaller import detect machinery to miss those libraries, failing the goal to build self-contained PyInstaller executables:

from ctypes import *
handle = CDLL("/usr/lib/library.so") # <- this will pass undetected under PyInstaller detect machinery, because it's not a direct import
handle.function_call()

Solution in PyInstaller

PyInstaller 1.4+ contains a pragmatic implementation of Ctypes dependencies: it will search for simple standard usages of ctypes and automatically track and bundle the referenced libraries. The following usages will be correctly detected:

CDLL("library.so")
WinDLL("library.so")
ctypes.DLL("library.so")
cdll.library # Only valid under Windows - a limitation of ctypes, not PyInstaller's
windll.library # Only valid under Windows - a limitation of ctypes, not PyInstaller's
cdll.LoadLibrary("library.so")
windll.LoadLibrary("library.so")

More in detail, the following restrictions apply:

  • only libraries referenced by bare filenames (e.g. no leading paths) will be handled; handling absolute paths would be impossible without modifying the bytecode as well (remember that while running frozen, ctypes would keep searching the library at that very absolute location, whose presence on the host system nobody can guarantee), and relative paths handling would require recreating in the frozen executable the same hierarchy of directories leading to the library, in addition of keeping track of which the current working directory is;
  • only library paths represented by a literal string will be detected and included in the final executable: PyInstaller import detection works by inspecting raw Python bytecode, and since you can pass the library path to ctypes using a string (that can be represented by a literal in the code, but also by a variable, by the return value of an arbitrarily complex function, etc...), it's not reasonably possible to detect all ctypes dependencies;
  • only libraries referenced in the same context of ctypes' invocation will be handled.

We feel that it should be enough to cover most ctypes' usages, with little or no modification required in your code.

Gotchas

The ctypes detect system at Analysis time is based on ctypes.util.find_library. This means that you have to make sure that while performing Analysis and running frozen, all the environment values find_library uses to search libraries are aligned to those when running un-frozen. Examples include using LD_LIBRARY_PATH/DYLD_LIBRARY_PATH to widen find_library scope.

Last modified 3 years ago Last modified on Nov 6, 2010 2:09:42 AM