The more common case for me is to name the parameters. Especially with longer variable names, this gets tedious fast. Given

    >>> very_long_var_name_1 = 'spam'
    >>> very_long_var_name_2 = 'ham'

compare

    >>> # Explicit but tedious and doesn't help readability:
    >>> print('{very_long_var_name_1}: {very_long_var_name_2}'.format(
    ...       very_long_var_name_1=very_long_var_name_1,
    ...       very_long_var_name_2=very_long_var_name_2))
    spam: ham

with

    >>> # Explicit but somehow feels dirty:
    >>> print('{very_long_var_name_1}: {very_long_var_name_2}'.format(
    ...       **locals()))
    spam: ham

and

    >>> # Still fits on one line. I think f prefix makes intent clear.
    >>> print(f'{very_long_var_name_1}: {very_long_var_name_2}')
    spam: ham