cannot use python in lua

[deejayd203]

i use a raspberry pi 2 and 3
if i do
py = require 'python'

this is what i get

py = require 'python'
stdin:1: module 'python' not found:
no field package.preload['python']
no file '/usr/local/share/lua/5.2/python.lua'
no file '/usr/local/share/lua/5.2/python/init.lua'
no file '/usr/local/lib/lua/5.2/python.lua'
no file '/usr/local/lib/lua/5.2/python/init.lua'
no file '/usr/share/lua/5.2/python.lua'
no file '/usr/share/lua/5.2/python/init.lua'
no file './python.lua'
no file '/usr/local/lib/lua/5.2/python.so'
no file '/usr/lib/arm-linux-gnueabihf/lua/5.2/python.so'
no file '/usr/lib/lua/5.2/python.so'
no file '/usr/local/lib/lua/5.2/loadall.so'
no file './python.so'
stack traceback:
[C]: in function 'require'
stdin:1: in main chunk
[C]: in ?

any help

[haianos]

Most likely, your LUA_CPATH has not been configured accordingly.

[Erf4nDev]

what should we do?

[greatwolf]

Two things come to mind, you can either move the python.so into one of the default search paths that Lua looks in(eg. from the stacktrace) or you can add the location where python.so exist to LUA_CPATH(as a shell's env variable). Or you can also append that path to package.cpath from Lua. For example

package.cpath = package.cpath .. ";/path_where_your/lunatic_python_binary_exist/goes_here/?.so"
py = require 'python'
-- ...

[Erf4nDev]

thanks i'll check

[aisurfer]

Hallo! I set LUA_CPATH as I see libs copied to site-packages
export LUA_CPATH="/usr/lib/python2.7/site-packages/?.so;;"
also change 'python' -> 'lua-python'
$ lua test_py.lua lua: error loading module 'lua-python' from file '/usr/lib/python2.7/site-packages/lua-python.so': /usr/lib/python2.7/site-packages/lua-python.so: undefined symbol: _Py_ZeroStruct stack traceback: [C]: in ? [C]: in function 'require' test_py.lua:1: in main chunk [C]: in ? Press any key to continue...

Weee new issue:) What does it mean? Is "lua-python.so" the right lib to use in lua scripts? Why it is installed in python2.7/site-packages ?
What should I do to fix?

Thanks in advance!

[hosford42]

My .so files had much longer names. I ended up running into the same issue as you, @surfindominator .

@greatwolf , is there something we're getting wrong? I'd be happy to work with you to figure this out so we can get everyone an answer.

[hosford42]

FYI, I'm using Python 3.5 on Ubuntu, with virtualenv. I'm curious what environments the other folks having this issue are using. Maybe there is a commonality?

[greatwolf]

What's the name of the lunatic .so built? What's the full path of its location? Also what version of lua/luajit is being used?

Note that lua C modules are sensitive to how the shared library is named. Specifically, the name of the *.so needs to match entry function eg. python.so needs to contain luaopen_python. If the .so file gets renamed you'll also have to update the entry function name too or lua will fail to load it.

[hosford42]

I'm using Lua 5.2.4. It builds two .so files:

copying build/lib.linux-x86_64-3.5/lua-python.cpython-35m-x86_64-linux-gnu.so -> /home/hosford4/.virtualenvs/testenv/lib/python3.5/site-packages
copying build/lib.linux-x86_64-3.5/lua.cpython-35m-x86_64-linux-gnu.so -> /home/hosford42/.virtualenvs/testenv/lib/python3.5/site-packages

I tried renaming each of them to python.so, and got the same error as @surfindominator for each file. I'm not sure how to go about renaming the entry function, but it looks like it's getting past that point considering the error message -- or maybe I'm misunderstanding.

[hosford42]

@greatwolf, I looked a little closer and realized the message is not identical. It's failing to resolve PyFloat_Type, not _Py_ZeroStruct. After a bit of googling, I suspect maybe the issue is that libpython is not being linked against.

[hosford42]

I think I found a bug in the setup.py script. In pkgconfig, the for loop that runs pkg-config breaks if the first call is successful. This means that the lua libs & cflags are captured, but the python libs & cflags are omitted. I modified the function to:

def pkgconfig(*packages):
    # map pkg-config output to kwargs for distutils.core.Extension
    flag_map = {'-I': 'include_dirs', '-L': 'library_dirs', '-l': 'libraries'}

    combined_pcoutput = ''
    for package in packages:
        (pcstatus, pcoutput) = commands.getstatusoutput(
            "pkg-config --libs --cflags %s" % package)
        if pcstatus == 0:
            combined_pcoutput += ' ' + pcoutput
        else:
            sys.exit("pkg-config failed for %s; "
                     "most recent output was:\n%s" %
                     (", ".join(packages), pcoutput))

    kwargs = {}
    for token in combined_pcoutput.split():
        if token[:2] in flag_map:
            kwargs.setdefault(flag_map.get(token[:2]), []).append(token[2:])
        else:                           # throw others to extra_link_args
            kwargs.setdefault('extra_link_args', []).append(token)

    if PY3:
        items = kwargs.items()
    else:
        items = kwargs.iteritems()
    for k, v in items:     # remove duplicated
        kwargs[k] = list(set(v))

    return kwargs

After making this change, and renaming the .so files to lua.so and lua-python.so according to the filename prefixes, I was able to get past the require statement without error.

[hosford42]

I submitted a pull request for the bug fix. This should resolve the linking issues. The .so naming issues are still outstanding.

[hosford42]

I'm running into a new issue now. After require executes successfully, the python global is nil. Any idea what might cause this?