Why does this python method gives an error saying global name not defined?

Question

I have a single code file for my Google App Engine project. This simple file has one class, and inside it a few methods. Why does this python method gives an error saying global name not defined?
Erro NameError: global name 'gen_groups' is not defined

import wsgiref.handlers


from google.appengine.ext import webapp
from django.utils import simplejson

class MainHandler(webapp.RequestHandler):

  def gen_groups(self, lines):
    """ Returns contiguous groups of lines in a file """

    group = []

    for line in lines:
      line = line.strip()
      if not line and group:
        yield group
        group = []
      elif line:
          group.append(line)

  def gen_albums(self, groups):
   """ Given groups of lines in an album file, returns albums  """

   for group in groups:
      title    = group.pop(0)
      songinfo = zip(*[iter(group)]*2)
      songs    = [dict(title=title,url=url) for title,url in songinfo]
      album    = dict(title=title, songs=songs)

      yield album





  def get(self):
    input = open('links.txt')
    groups = gen_groups(input)
    albums = gen_albums(groups)

    print simplejson.dumps(list(albums))



def main():
  application = webapp.WSGIApplication([('/', MainHandler)],
                                       debug=True)
  wsgiref.handlers.CGIHandler().run(application)


if __name__ == '__main__':
  main()

Answer 1

You need to call it explicitly with an instance:

groups = self.gen_groups(input)

Similarly for some of the other calls you're making in there, e.g. gen_album.

Also, see Knowing When to Use self and __init__ for more information.

Answer 2

It's an instance method, you need to use self.gen_groups(...) and self.gen_albums(...).

Edit: I'm guessing the TypeError you are getting now is because you removed the 'self' argument from gen_groups(). You'll need to put it back in:

def get_groups(self, lines):
    ...

Answer 3

You have to use it like this:

self.gen_groups(input)

There is not implicit "self" in Python.