Python Width and Precision:

A conversion specifier may include a field width and a precision. 

The width is the minimum number of characters reserved for a formatted value. The precision is (for a numeric conver-sion) the number of decimals that will be included in the result or (for a string conversion) the maximum number of characters the formatted value may have.

These two parameters are supplied as two integer numbers (width first, then precision), 

separated by a . (dot). Both are optional, but if you want to supply only the precision, 

you must also include the dot:

>>> '%10f' % pi      # Field width 10

'  3.141593'

>>> '%10.2f' % pi    # Field width 10, precision 2

'      3.14'

>>> '%.2f' % pi      # Precision 2

'3.14'

>>> '%.5s' % 'Guido van Rossum'

'Guido'

You can use an * (asterisk) as the width or precision (or both). 

In that case, the number will be read from the tuple argument:

>>> '%.*s' % (5, 'Guido van Rossum')

'Guido'