python bisect questions

[ankitks.mital at gmail.com]

I am week on functional programming, and having hard time
understanding this:

class myPriorityQueue:
      def __init__(self, f=lamda x:x):
              self.A = []
              self.f = f

      def append(self, item)
              bisect.insort(self.A, (self.f(item), item))
    ............

now I know we are inserting items(user defined type objects) in list A
base on sorting order provided by function A.
but what I don't understand is bisect command
what does bisect.insort(self.A, (self.f(item), item)) doing

isn't it is returning truple of (self.f(item), item)).
why it is not
biset.insort(self.A, item)
A.sort(f)

thanks for your comments