Question

How I can fix it?

return 'loader:\n {}' % ''.join('{}:{}\n'.format(*(key, value) for key, value in slownik.iteritems()))

SyntaxError: invalid syntax

this should be in one line 😉

Answer 1

Drop the ‘%’, which is the old-style string formatter; drop the generator comprehension, because iteritems returns exactly what you need to do formatting; finally, drop the double format:

'loader:\n {0}:{1}\n'.format(*slownik.iteritems())

EDIT: ok, now I see what you want to do.

'loader:\n' + ''.join(' {0}:{1}\n'.format(k, v)
                      for k, v in slownik.iteritems())