The Pitfalls of Integrating Lua
with Python

郭學聰 Hsueh-Tsung Kuo
Sat, 2 Oct 2021

The Pitfalls of Integrating Lua with Python 郭學聰 Hsueh-Tsung Kuo Sat, 2 Oct 2021 CC BY-SA 4.0

	-- defines a factorial function
	function fact (n)
	if n == 0 then
	return 1
	else
	return n * fact(n-1)
	end
	end

	print("enter a number:")
	a = io.read("*number") -- read a number
	print(fact(a))

	#!/usr/bin/env python3
	# -- coding: utf-8 --


	# from https://alchemypy.com/2020/05/13/speed-your-python-with-lua/


	import sys
	import time

	from lupa import LuaRuntime


	def sum_all_to_range_pure_python(end_range_number):
	start_time = time.time()
	the_sum = 0
	for number in range(1, end_range_number+1):
	the_sum += number
	stop_time = time.time()
	return (end_range_number, stop_time - start_time, the_sum)


	def sum_all_to_range_with_lua_python(end_range_number):
	start_time = time.time()

	lua_code = """
	function(n)
	sum = 0
	for i=1,n,1 do
	sum = sum + i
	end
	return sum
	end
	"""
	lua_func = LuaRuntime(encoding=None).eval(lua_code)
	the_sum = lua_func(end_range_number)
	stop_time = time.time()
	return(end_range_number, stop_time - start_time, the_sum)


	def main(argv=sys.argv[:]):
	end_range_number = 200000000

	python_result = sum_all_to_range_pure_python(end_range_number)
	lupa_result = sum_all_to_range_with_lua_python(end_range_number)

	print('python - range: %d, time: %g sec, sum: %d' % python_result)
	print('lupa - range: %d, time: %g sec, sum: %d' % lupa_result)


	if __name__ == '__main__':
	sys.exit(main())

	>>> import lupa
	>>> from lupa import LuaRuntime
	>>> lua = LuaRuntime(unpack_returned_tuples=True)

	>>> lua.eval('1+1')
	2

	>>> lua_func = lua.eval('function(f, n) return f(n) end')

	>>> def py_add1(n): return n+1
	>>> lua_func(py_add1, 2)
	3

	>>> lua.eval('python.eval(" 2 ** 2 ")') == 4
	True
	>>> lua.eval('python.builtins.str(4)') == '4'
	True

	>>> lua_func = lua.eval('function(obj) return obj["get"] end')
	>>> d = {'get' : 'value'}

	>>> value = lua_func(d)
	>>> value == d['get'] == 'value'
	True

	>>> value = lua_func( lupa.as_itemgetter(d) )
	>>> value == d['get'] == 'value'
	True

	>>> dict_get = lua_func( lupa.as_attrgetter(d) )
	>>> dict_get == d.get
	True
	>>> dict_get('get') == d.get('get') == 'value'
	True

	>>> lua_func = lua.eval(
	... 'function(obj) return python.as_attrgetter(obj)["get"] end')
	>>> dict_get = lua_func(d)
	>>> dict_get('get') == d.get('get') == 'value'
	True

	>>> lua.execute('''
	... for i in python.iter(python.builtins.dir(python.builtins)) do
	... print(i)
	... end
	... ''')
	ArithmeticError
	AssertionError
	AttributeError
	BaseException
	.
	.
	.
	map
	max
	memoryview
	min
	next
	object
	oct
	open
	ord
	pow
	print
	property
	quit
	range
	repr
	reversed
	round
	set
	setattr
	slice
	sorted
	staticmethod
	str
	sum
	super
	tuple
	type
	vars
	zip

	LUA_ISOLATED_RUNTIME_SCRIPT = '''
	require = nil
	package = nil

	os = nil
	io = nil

	python = nil
	'''

	lua.execute(LUA_ISOLATED_RUNTIME_SCRIPT)

	import luadata

	def convert_table_to_dict(table):
	dict_data = {}
	for (k, v) in table.items():
	if lupa.lua_type(v) == 'table':
	vd = convert_table_to_dict(v)
	else:
	vd = v
	dict_data[k] = vd
	return dict_data

	dict_data = {'a': 1, 'b': 2, 'c': {'d': 4, 'e': 5, 'f': 6}}
	table = lua.eval(luadata.serialize(dict_data)) # convert dict to table
	result_table = lua_func(table)
	result_dict_data = convert_table_to_dict(result_table)

	LUA_UTIL_FUNC_SCRIPT = '''
	function get_table_size(tbl)
	local count = 0
	for _ in pairs(tbl) do
	count = count + 1
	end
	return count
	end

	function clear_table(tbl)
	for k, v in pairs(tbl) do
	tbl[k] = nil
	end
	end

	function get_table(tbl, k, default)
	local v = tbl[k]
	if v == nil then
	v = default
	end
	return v
	end

	function set_default_to_table(tbl, k, default)
	if tbl[k] == nil then
	tbl[k] = default
	end
	return tbl[k]
	end
	'''

	lua.execute(LUA_UTIL_FUNC_SCRIPT)

	import lupa, luadata
	from lupa import LuaRuntime
	lua = LuaRuntime(unpack_returned_tuples=True)

	def convert_table_to_dict(table):
	dict_data = {}
	for (k, v) in table.items():
	if lupa.lua_type(v) == 'table':
	vd = convert_table_to_dict(v)
	else:
	vd = v
	dict_data[k] = vd
	return dict_data

	def convert_dict_to_table(dict_data):
	return lua.eval(luadata.serialize(dict_data))

	LUA_ISOLATED_RUNTIME_SCRIPT = '''
	require = nil
	package = nil

	os = nil
	io = nil

	python = nil
	'''

	lua.execute(LUA_ISOLATED_RUNTIME_SCRIPT)

	LUA_UTIL_FUNC_SCRIPT = '''
	function get_table_size(tbl)
	local count = 0
	for _ in pairs(tbl) do
	count = count + 1
	end
	return count
	end

	function clear_table(tbl)
	for k, v in pairs(tbl) do
	tbl[k] = nil
	end
	end

	function get_table(tbl, k, default)
	local v = tbl[k]
	if v == nil then
	v = default
	end
	return v
	end

	function set_default_to_table(tbl, k, default)
	if tbl[k] == nil then
	tbl[k] = default
	end
	return tbl[k]
	end
	'''

	lua.execute(LUA_UTIL_FUNC_SCRIPT)

	# test

	dict_data = {'a': 1, 'b': 2, 'c': {'d': 4, 'e': 5, 'f': 6}}

	tbl = lua.eval('{a = 1, b = 2, c = {d = 4, e = 5, f = 6}}')

	lua_func = lua.eval('''
	function(tbl)
	print(tbl)
	for k, v in pairs(tbl) do
	print(string.format("%s %s", k, v))
	end
	return tbl
	end
	''')