Formulas of interpolation/extrapolation method spline

Questions
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1

Hello,

I would like to understand the formula behind the following interpolation and extrapolation done in mathematica in order to convert it in python:

K is equal to

{27.827, 18.53, -30.417}	0.205
{22.145, 13.687, -33.282}	0.197
{29.018, 18.841, -38.761}	0.204
{26.232, 22.327, -27.735}	0.197
{28.761, 21.565, -31.586}	0.212
{24.002, 17.759, -24.782}	0.208
{17.627, 18.224, -25.197}	0.204
{24.834, 20.538, -33.012}	0.205
{23.017, 23.037, -29.23}	0.211
{26.263, 23.686, -32.766}	0.215

K = ToExpression[Import[NotebookDirectory[] <> "df.txt", "TSV"]];
func = Interpolation[Map[{#[[1]], #[[2]]} &, K], 
   InterpolationOrder -> {1, 1, 1}, Method -> "Spline"];

result= func[2, 2, -3]
0.0298707

result1 = func[20,20,-30]
0.168097

To have these results which is the formula applied using the variables above?
Thanks