iterator? way of generating all possible combinations?

[akameswaran at gmail.com]

Scott David Daniels wrote:
> Sorry, "re-iterables".  A file re-iterable is:
>
>      class FileReIterable(object):
>          def __init__(self, file):
>              if isinstance(file, basestring):
>                  self.file = open(file, 'rU')
>              else:
>                  self.file = file
>          def __iter__(self):
>              self.file.seek(0)
>              return iter(self.file)
>
> This works if-and-only-if it is only in use once at a time.
> If you have multiple simultaneous accesses, you need to do
> something like:
>
>      class FileReIterable2(object):
>          def __init__(self, file):
>              if isinstance(file, basestring):
>                  self.file = open(file, 'rU')
>              else:
>                  self.file = file
>          def __iter__(self):
>              self.file.seek(0)
>              for line in self.file:
>                  nextpos = self.file.tell()
>                  yield line
>                  self.file.seek(nextpos)
>
> --Scott David Daniels
> scott.daniels at acm.org

Since I was doing this as a self education excercise.  When you say is
in use once and only once, you mean I can only use a single instance of
the class?  I haven't even tested these yet, but I am very curious
about that statement.  Why is it necessary to return a generator object
in the second example?  If it's a real long explanation, feel free to
point me to some relvant texts.   My practical problem was solved about
10 posts ago... but I am still trying to understand the behavior.

Thank you for you time.

AK