Using python str.format(*args) when the cardinality of *args is unknown

Python 3's str.format() function inserts its arguments into replacement fields delimited by braces {} in the string str. The arguments of format() can include tuple- or keyword-arguments whose length may be uncertain before runtime, and they will be unpacked when format() is actually called.

However, even if the arguments are of uncertain number, it seems to me that the bracket-delimited replacement fields in str are normally not. Only if the string is constructed by concatenation in response to the number of arguments of format is it possible for each of those arguments to be assured a corresponding replacement field:

In [1]: user_input = input('What did R. Crumb say? ')
Out[1]: What did R. Crumb say? Are the lumpen proletariat a lost cause?

In [2]: variable_length_args = user_input.split()
In [3]: the_string = [str(i) for i in range(len(variable_length_args))]

In [4]: the_string = '"{' + '}" and "{'.join(the_string) + '}"'
In [5]: the_string.format(\*variable_length_args)
Out[5]: '"Are" and "the" and "lumpen" and "proletariat" and "a" and "lost" and "cause?"'

Or is there some other special syntax for ensuring the right number of replacement fields, if that number is not known until runtime?

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