lua-python import error

[Vogen]

I use cmake ./ and make to build lua.so and 'python.so'. And error occur while using.

user@host:~$ cat test.lua
python = package.loadlib("/path/to/lunatic-python/bin/lua.so", "luaopen_python")()
python.execute("import os")
python.execute("import multiprocessing")
user@host:~$ lua test.lua
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/multiprocessing/__init__.py", line 84, in <module>
    import _multiprocessing
ImportError: /usr/lib/python2.7/lib-dynload/_multiprocessing.x86_64-linux-gnu.so: undefined symbol: _Py_ZeroStruct

Actually, I don't know what is the right way to build and to use .so file.

[greatwolf]

Try running package.loadlib on the python-2.7 runtime first. eg.

package.loadlib("libpython2.7.so", "*")
py = require 'python'
-- ...

That'll force dlopen to load the python-2.7 runtime and its symbols globally(w/ RTLD_GLOBAL) otherwise when the multiprocess module loads, those python api functions won't be visible. Strangely, Python 3.5 doesn't seem to need this.

[Vogen]

@greatwolf
it doesn't work.

usr@host:~$ cat test.lua
package.loadlib("/usr/lib/python2.7/config-x86_64-linux-gnu/libpython2.7.so", "*")
py = require "python"
py.execute("import os")
py.execute("import multiprocessing")

usr@host:~$ lua test.lua
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/multiprocessing/__init__.py", line 84, in <module>
    import _multiprocessing
ImportError: /usr/lib/python2.7/lib-dynload/_multiprocessing.x86_64-linux-gnu.so: undefined symbol: _Py_ZeroStruct

[greatwolf]

Make sure you're running this on at least lua5.2. lua 5.1's package.loadlib doesn't support that signature.

[Vogen]

Sad, I use lua5.1. How to solve it?

[greatwolf]

There's a PR #37 that you could try. I haven't got around to testing it yet so dunno if it works.

[Vogen]

I run the code on lua5.2 successfully. And I want to build lunatic-python with luajit source code. Could you give me any advice?

[greatwolf]

The rough steps to build on linux are:

• install luajit with apt-get.
• install libluajit-5.1-dev needed to build lunatic.
• install cmake
• build lunatic using cmake; an out-of-source build is recommended
• use -DCMAKE_PREFIX_PATH, -DPYTHON_LIBRARY and -DLUA_LIBRARY to point cmake on which lua and python runtime to link against.

For example, the following builds for me on linux lite:

cmake -B./build -H. -DPYTHON_LIBRARY=/usr/lib/i386-linux-gnu/libpython2.7.so -DLUA_LIBRARY=/usr/lib/i386-linux-gnu/libluajit-5.1.so -DCMAKE_PREFIX_PATH="/usr/include/python2.7;/usr/include/luajit-2.0"
cmake --build ./build

After config'ing but before running build, you might want to spot check the cmake config output to make sure the dependencies match up. Make sure the "found suitable version" matches up with what the version you expect for Python and Lua. Make sure the .so is the same one you passed in if you explicitly specified one to use through LUA_LIBRARY and PYTHON_LIBRARY.

If all goes well the compiled modules lua.so/python.so will be in ./build/bin.

[Vogen]

Thank you @greatwolf , It works!

[greatwolf]

no problem. I'm closing this issue unless there's something else.