[Tutor] Generator questions.

[rumpy at mrbitter.org]

Hi Folks,


I'm working through Magnus Lie Hetland's excellent book "Beginning 
Python" and I have a few basic (I think) questions. Specifically, 
regarding his first project in Chapter 20(Instant Markup).

The outline of the project is to take a plain text file and "mark it 
up" into HTML or XML. Step one is simply getting the tool to recognize 
basic elements of a text document - blocks of text seperated by empty 
lines.

To this end the following file is created as a module(?) to be imported 
into the
subsequent primary execution (main?) script.


def lines(file):
   for line in file: yield line
   yield '\n'

del blocks(file):
   block = []
   for line in lines(file):
       if line.strip():
          block.append(line)
       elif block:
          yield ''.join(block).strip()
          block = []


Now, for the most part I understand what's going on here. The part that 
puzzles me a bit is:

elif block:
  yield ''.join(block).strip()
  block = []

1.) Does the yield mean the block list is returned from the function 
AND then wiped out by 'block = []'?

2.) Is block list scrubbed clean by 'block = []' because the function 
is going to iterate over the next block and it needs to be empty?

3.) The statement after the 'yield' threw me. I haven't seen that to 
this point in the book. I figured 'yield' is always last in a function 
because it needs to iterate over itself again. Am I understanding 
generators correctly?

4.) Is it correct to say that a generator is a function that returns 
multiple values and iterates over itself?


Thanks in advance for any feedback/help.


Rumpy.