How to align positive and negative values along the decimal point in python

Question

I want to write bunch of positive and negative values into a text file as below

1      12.203026     2.291063     -0.061603
1      -0.736147     1.353548     -1.347932
6       0.728048     1.348907      0.247566
6      -0.728048     1.348907    -10.247565
1      10.736147     1.353547      1.347932
1      -1.203026    12.291063      0.061604
6      11.583889     0.179143    -10.258947

when I am writing that it should be aligned along the decimal points as above. The code I written using following f.write() command and it's out put as below.

 f.write('%s    %2.6f   %2.6f   %2.6f\n' % (a, x, y, z ))

out put

1      12.203026    2.291063    -0.061603
1      -0.736147    1.353548    -1.347932
6      0.728048     1.348907    0.247566
6      -0.728048    1.348907    -10.247565
1      10.736147    1.353547    1.347932
1      -1.203026    12.291063    0.061604
6      11.583889    0.179143    -10.258947

Answer 1

The first number in the format is the total number of characters, not the number before the decimal point. When that number is too small it compensates by dropping all the padding. To get what you want you need to use %10.6f, not %2.6f. That's 1 for the -, 2 for the initial digits, 1 for the decimal point, and 6 digits after the decimal - 1+2+1+6=10.

Answer 2

Suppose I have:

>>> li=[['1', 12.203026, 2.291063, -0.061603], ['1', -0.736147, 1.353548, -1.347932], ['6', 0.728048, 1.348907, 0.247566], ['6', -0.728048, 1.348907, -10.247565], ['1', 10.736147, 1.353547, 1.347932], ['1', -1.203026, 12.291063, 0.061604], ['6', 11.583889, 0.179143, -10.258947]]

You can right align into a fixed field width in two steps:

for a,x,y,z in li:
    x1, y1, z1=['{:2.6f}'.format(e) for e in (x,y,z)]
    print '{} {:>13} {:>13} {:>13}'.format(a, x1, y1, z1 )

Prints:

1     12.203026      2.291063     -0.061603
1     -0.736147      1.353548     -1.347932
6      0.728048      1.348907      0.247566
6     -0.728048      1.348907    -10.247565
1     10.736147      1.353547      1.347932
1     -1.203026     12.291063      0.061604
6     11.583889      0.179143    -10.258947

If you want to specify width and precision in one place, you can do:

'{} {:{w}.{p}f} {:{w}.{p}f} {:{w}.{p}f}'.format(a, x, y, z, w=13, p=6 )