The difference between .format and round ()

>>> a=3.12
>>> print(round(a,2))
3.12
>>> print(round(a,1))
3.1

>>>  print('{:.2f}'.format(a))
3.12
>>>  print('{:.1f}'.format(a))
3.1

>>> b=3.1
>>>  print(round(b,2))
3.1
>>>  print(round(b,1))
3.1

>>> print('{:.2f}'.format(b))
3.10
>>> print('{:.1f}'.format(b))
3.1