How to interpolate for 0 between three values in python?

Say I have three columns

1,2,3 with values -5, 5, 15

I need to find where 0 lies between the columns and make it a new column

Here the answer would be 1.5 (halfway between column 1 and 2)

How to do linear interpolation in python to do this for many rows?

Needs to incorporate all 3 columns, so could get an answer like 2.2

If greater than 3, can extrapolate or otherwise just put 3 or na

Thanks!

You can use numpy.interp for each row. If the target is outside the bounds, you'll get the closest x value.

Example:

df = pd.DataFrame([[-5, 5, 15], [-5, -2, 6],[1, 2, 3], [-3, -2, -1]],
                  columns=[1,2,3])

df['x_at_0'] = [np.interp(0, xp, df.columns) for xp in df.to_numpy()]

Output:

   1  2   3  x_at_0
0 -5  5  15    1.50
1 -5 -2   6    2.25
2  1  2   3    1.00
3 -3 -2  -1    3.00