>>> def gen():
... yield 1
... yield 2
... yield 3
...
>>> type(gen)

>>> g.next()
1
>>> g.next()
2
>>> g.next()
3
>>> g.next()
Traceback (most recent call last):
File "", line 1, in
StopIteration


Basically, gen is just a function. It’s the yield statements that let python know it’s a generator. g is the actual generator object created from calling gen().

Calling g.next() the first time returns the first value that’s “yielded”. The second time, the function just picks up where it left off, so g.next() returns 2, etc. Until it drops off the end, at which point it raises a StopIteration exception. This is kind how iterators work behind the scenes. Generators make it easier to write iterators without defining a class and the next, iter methods.

You don’t usually use a generator in that way. Instead you would use it like an iterator, like this:


>>> for num in gen():
... print num
...
1
2
3


Anyway, to your post … showlinks() returns a generator object, and you could call next() or just iterate through it with a for loop.

When you create a list (links = list(showlinks())), it’s basically iterated through the entire generator and stuffed the values in that list.

Each element of the list is actually a an instance of the Link class from the mechanize package (twill is using mechanize for its browsing facilities):


>>> link = links[1]
>>> link
Link(base_url='http://del.icio.us', url='https://secure.del.icio.us/login', text='login',
tag='a', attrs=[('href', 'https://secure.del.icio.us/login')])
>>> type(link)

>>> dir(link)
['__cmp__', '__doc__', '__init__', '__module__', '__repr__', 'absolute_url', 'attrs', 'bas
e_url', 'tag', 'text', 'url']
>>> link.url
'https://secure.del.icio.us/login'
>>> link.text
'login'
>>> link.absolute_url
'https://secure.del.icio.us/login'
>>> link.tag
'a'


Hope that makes sense.

1. None ==> /20484

Where the number is dynamically generated. I am not sure how to follow that link.