print a variable field width in an f-string code example

Example 1: f string float format

>>> a = 10.1234
>>> f'{a:.2f}'
'10.12'

Example 2: python f-string padding

#!/usr/bin/env python3

name = 'Peter'
age = 23

print('%s is %d years old' % (name, age))
print('{} is {} years old'.format(name, age))
print(f'{name} is {age} years old')