Mark Cidade's answer is right - you need to supply a tuple.

However from Python 2.6 onwards you can use format instead of %:

'{0} in {1}'.format(unicode(self.author,'utf-8'),  unicode(self.publication,'utf-8'))

Usage of % for formatting strings is no longer encouraged.

This method of string formatting is the new standard in Python 3.0, and should be preferred to the % formatting described in String Formatting Operations in new code.

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)

"{0} {1} {1}".format("foo", "bar")

You were almost there, just remove the comma (and pass in a float number, not a string):

"{0:>15.2f}".format(1464.1000000000001)

See the Format Specification Mini-Language section:

format_spec ::=  [[fill]align][sign][#][0][width][,][.precision][type]
fill        ::=  <any character>
align       ::=  "<" | ">" | "=" | "^"
sign        ::=  "+" | "-" | " "
width       ::=  integer
precision   ::=  integer
type        ::=  "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"

Breaking the above format down then:

fill: <empty>
align: <  # left
sign: <not specified>
width: 15
precision: 2
type: `f`

Demo:

>>> "{0:>15.2f}".format(1464.1000000000001)
'        1464.10'

Note that for numbers, the default alignment is to the right, so the > could be omitted.

You could use the str.format() function, that allows named arguments, so:

'''line {0}
line {1}
line {2}'''.format(1,2,3)

You could of course extend this using Python's *args syntax to allow you to pass in a tuple or list:

args = (1,2,3)
'''line {0}
line {1}
line {2}'''.format(*args)

If you can intelligently name your arguments, the most robust solution (though the most typing-intensive one) would be to use Python's **kwargs syntax to pass in a dictionary:

args = {'arg1':1, 'arg2':2, 'arg3':3}
'''line {arg1}
line {arg2}
line {arg3}'''.format(**args)

For more information on the str.format() mini-language, go here.