combining python lists in savetxt

Question

I have 2 python lists that I want to save side by side using np.savetxt().

I have tried:

np.savetxt('./filename.txt',np.hstack([list1,list2]),fmt=['%f','%f'])

but I get the error message

raise AttributeError('fmt has wrong shape.  %s' % str(fmt))
AttributeError: fmt has wrong shape.  ['%f', '%f']

I don't know if it is relevant, but the lists are in decimal.Decimal format.

What am I doing wrong please?

---

edit: I originally said "vstack" but I meant "hstack".

Answer 1

Just pass a single value to fmt , like this:

np.savetxt('./filename.txt',np.vstack([list1,list2]),fmt='%f')

Example:

import decimal, numpy as np
a = np.array([decimal.Decimal("1.0"),
              decimal.Decimal("2.0"),
              decimal.Decimal("3.0")],
             dtype=np.dtype(decimal.Decimal))
b = a + 1
np.savetxt('./filename.txt',np.vstack([a, b]),fmt='%f')

The resulting file looks like this:

1.000000 2.000000 3.000000
2.000000 3.000000 4.000000