##
4.7.2 Keyword Arguments

Functions can also be called using keyword arguments of the form "`keyword = value`". For instance, the following function:

      def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
          print "-- This parrot wouldn't", action,
          print "if you put", voltage, "Volts through it."
          print "-- Lovely plumage, the", type
          print "-- It's", state, "!"

could be called in any of the following ways:

      parrot(1000)
      parrot(action = 'VOOOOOM', voltage = 1000000)
      parrot('a thousand', state = 'pushing up the daisies')
      parrot('a million', 'bereft of life', 'jump')

but the following calls would all be invalid:

      parrot()                     # required argument missing
      parrot(voltage=5.0, 'dead')  # non-keyword argument following keyword
      parrot(110, voltage=220)     # duplicate value for argument
      parrot(actor='John Cleese')  # unknown keyword

In general, an argument list must have any positional arguments followed by any keyword arguments, where the keywords must be chosen from the formal parameter names. It's not important whether a formal parameter has a default value or not. No argument must receive a value more than once -- formal parameter names corresponding to positional arguments cannot be used as keywords in the same calls.

When a final formal parameter of the form `**name` is present, it receives a dictionary containing all keyword arguments whose keyword doesn't correspond to a formal parameter. This may be combined with a formal parameter of the form `*name`(described in the next subsection) which receives a tuple containing the positional arguments beyond the formal parameter list. (`*name` must occur before `**name`.) For example, if we define a function like this:

      def cheeseshop(kind, *arguments, **keywords):
          print "-- Do you have any", kind, '?'
          print "-- I'm sorry, we're all out of", kind
          for arg in arguments: print arg
          print '-'*40
          for kw in keywords.keys(): print kw, ':', keywords[kw]

It could be called like this:

      cheeseshop('Limburger', "It's very runny, sir.",
                 "It's really very, VERY runny, sir.",
                 client='John Cleese',
                 shopkeeper='Michael Palin',
                 sketch='Cheese Shop Sketch')

and of course it would print:

      -- Do you have any Limburger ?
      -- I'm sorry, we're all out of Limburger
      It's very runny, sir.
      It's really very, VERY runny, sir.
      ----------------------------------------
      client : John Cleese
      shopkeeper : Michael Palin
      sketch : Cheese Shop Sketch