Inner classes

[Isaac To]

>>>>> "Andrew" == Andrew Kuchling <akuchlin at mems-exchange.org> writes:

    Andrew> xyzmats at laplaza.org (Mats Wichmann) writes:
    >> Nonetheless, I was challenged by someone to describe how it isn't a
    >> shorcoming in Python that classes don't work this way and didn't
    >> convince the guy so I'm looking for a more erudite comparison.

    Andrew> Work *what* way?  It's perfectly legal to do this:

    Andrew> class C: class inner: ... stuff for inner class ... stuff for
    Andrew> class C

No if the original poster wants a Java-style inner class.  Java inner class
is a rather strange concept.  The idea is for the inner class instance to
have a reference to the outer class, and unlock the namespace of the outer
class in methods of the inner class.  It works like this in Python syntax:

class outer:
  def __init__(self):
    self.d = 2
  def f(self):
    print self.d
  # The following does not exist in Python
  class inner:
    def __init__(self):
      # should already got a hidden reference to an outer instance
      self.d2 = 5   # can also have its own data
    def g(self):
      print self.d  # should print the d of outer reference
      self.f()      # should call f for the outer reference
      print self.d2 # print d2 of inner
  def h(self):      # return instance of inner class
    return self.inner()

x=outer() # create instance
y=x.h()   # y is an inner instance
y.g()     # print 2 twice and then 5

Of course, currently the above says "Attribute Error: x" in the last line.

Regards,
Isaac.