There are many ways to pass actual parameters in Lua.

Consider the following program. All ways of calling result in the same output. There are many variations of these methods.

• An ordered list of parameters is designated with the single asterisk "*".
• An dictionary of named parameters is designated with the double asterisk "**".

Here is the Python code [#1]
def action1(a1, b1, c1, d1): print("a=[{0:s}] b=[{1:s}] c=[{2:s}] d=[{3:s}]".format(a1,b1,c1,d1)) w1="one" x1="two" y1="three" z1="four" list1 = [w1, x1, y1, z1] dict1 = { "a1" : w1, "b1" : x1, "c1" : y1, "d1" : z1, } list2 = [w1, x1] dict2 = {"c1" : y1, "d1" : z1, } # pass explicit args (position order) action1(w1,x1,y1,z1) # pass named args (any order) action1(a1=w1,b1=x1,c1=y1,d1=z1) # pass args list using * (position order element in list) action1(*list1) # pass kwargs dict using ** (any order by key in dict) action1(**dict1) # pass some by args using *, rest by kwargs using ** action1(*list2,**dict2)
Here is the output of the Python code.
a=[one] b=[two] c=[three] d=[four] a=[one] b=[two] c=[three] d=[four] a=[one] b=[two] c=[three] d=[four] a=[one] b=[two] c=[three] d=[four] a=[one] b=[two] c=[three] d=[four]

The kwargs way of passing parameters is especially useful in, say, a class method or module routine whereby there are a huge number of possible parameters, with defaults.

Adding another parameter then is easy and scales up to large number of parameters.