>>> import math
>>> x = [1, 2, 3, 1e11]
>>> y = map(math.sqrt, x)
>>> y
[1.0, 1.4142135623730951, 1.7320508075688772, 316227.76601683791]
>>> writedat("sqrt.dat", x, y)
>>> # check
...
>>> for line in open('sqrt.dat'):
...   print line,
...
1       1
2       1.4142
3       1.7321
1e+011  3.1623e+005