I had a look into the io.array_import.py and did the following modification : def str_array(arr, precision=5,col_sep=' ',row_sep="\n",ss=0): --> added if precision > -1 : fmtstr = "%%.%de" % precision else : fmtstr = "%f" And now I have what I need when I use io.write_array(file,array,precision=-1) Jaonary