Question

Consider this line in the pygame loop:

pygame.display.set_mode().fill((0, 200, 255))

From: http://openbookproject.net/thinkcs/python/english3e/pygame.html

I. How are you supposed to know there even is a fill function nested in set_mode? I searched in the pygame documentation and there is no information on fill in the set_mode section.

II. set_mode() is a function of the display module of the pygame package. How can I call a function nested in another function?
How could I call print"hi" with this function(tried it but get an AttributeError):

def f():
    def g():
        print "hi"

Answer 1

The pygame.display.set_mode() returns a Surface object.

From the documentation:

pygame.display.set_mode initialize a window or screen for display
pygame.display.set_mode(resolution=(0,0), flags=0, depth=0): return Surface

So you are calling the method .fill() on the surface object, not on the function set_mode().

You can find the methods available on surface objects in the surface documentation of pygame.

You cannot call a nested function in that way.
To get your desired result in your print example, you can use classes in the following way:

class F():
  def g(self):
    print "hi"

Resulting in:

>>> F().g()
hi

This is a simplified example to show how the display.set_mode().fill() works:

class Surface():
    def fill(self):
        print "filling"

class Display():
    def set_mode(self):
        return Surface()


Display().set_mode().fill()

Edit:

You can use nested functions, but it works slightly different from how you would do it with objects and modules:

def f():
  def g():
    print "hi"
  return g

Resulting in:

>>> outerf = f()
>>> outerf()
hi