python - How to format variable number of arguments into a string?

Question

We know that formatting one argument can be done using one %s in a string:

>>> \"Hello %s\" % \"world         


        

Answer 1

You'd use str.join() on the list without string formatting, then interpolate the result:

"Hello %s" % ', '.join(my_args)

Demo:

>>> my_args = ["foo", "bar", "baz"]
>>> "Hello %s" % ', '.join(my_args)
'Hello foo, bar, baz'

If some of your arguments are not yet strings, use a list comprehension:

>>> my_args = ["foo", "bar", 42]
>>> "Hello %s" % ', '.join([str(e) for e in my_args])
'Hello foo, bar, 42'

or use map(str, ...):

>>> "Hello %s" % ', '.join(map(str, my_args))
'Hello foo, bar, 42'

You'd do the same with your function:

function_in_library("Hello %s", ', '.join(my_args))

If you are limited by a (rather arbitrary) restriction that you cannot use a join in the interpolation argument list, use a join to create the formatting string instead:

function_in_library("Hello %s" % ', '.join(['%s'] * len(my_args)), my_args)