I use numpy
fname = r"c:\temp\space.txt"
a = np.loadtxt(fname, delimiter=" ")
outname = fname[:-3] + "csv"
np.savetxt(outname, a, fmt='%f', delimiter=", ")
a text file
1.0 2.0 3.0
4.0 5.0 6.0
as csv file
1.000000, 2.000000, 3.000000
4.000000, 5.000000, 6.000000
you can format as you see fit.
... sort of retired...