3 ms·

I'd been wondering why _source was in there. I'm a little surprised that Hettinger thinks it's so important to retain it. It's a neat demonstration of how to

I'd been wondering why _source was in there. I'm a little surprised that Hettinger thinks it's so important to retain it. It's a neat demonstration of how to make a new data type, and I like that it's so straightforward, but I don't buy the argument that slowing down the interpreter is important for didactic reasons. Edit: I'm talking about namedtuple, the implementation of which is slow because namedtuple() has to construct _source for every new namedtuple type. Which was clear from the article but not from my comment.

dr_zoidberg 9y ago
Actually your edit made it clearer from both. I had the feeling that namedtuply was constructing _source, but it wasn't obvious in the article either. So thanks for explaining, both your comment and the article.
mnarayan01 9y ago
Yea I'm not getting the need to keep _source in collections.namedtuple at all. For teaching purposes, you can just present the existing implementation...I don't see what purpose having that teaching code be in the core distribution serves?
- xapata 9y ago
  Not everyone is familiar with looking at the core source, or even reading the docs.
- takeda 9y ago
  In case you overlooked, Raymond H explained it in another thread[1]. [1] https://news.ycombinator.com/item?id=15135569 https://news.ycombinator.com/item?id=15135569
raymondh 9y ago
One purpose of _source is to make the namedtuple self-documenting -- that has been a considerable benefit over the years and has resulted in many fewer questions and issues than we usually get about our other tools. Another purpose of _source is so that you can write it out to a module. This lets you pre-compute the named tuple for speed and it makes it possible to easily Cythonize it or to customize it (in particular, people like to take out the error checking). Since the namedtuple() factory function was already creating the source string as part of its operation, just storing it and exposing the attribute had nearly zero additional cost. That said, don't worry about it, next week I plan to make this a lazily generated attribute so you all can sleep soundly at night :-)
- stuaxo 9y ago
  It's interesting + quite nice implementation. I've been using python for 10 years, and vaguely knew namedtuple used exec, but never knew there was a _source attribute. I'm definitely looking forward to faster startup though. I also didn't realise you can't pickle namedtuple by default, which probably cost me a few days on a project, don't think I tracked this down as the reason, but it makes sense now.
- nerdponx 9y ago
  Does this mean you're changing how Namedtuples are implemented, or just not saving _source?
  - deleted 9y ago
    [deleted]
- sevensor 9y ago
  Thanks for the clarification! It makes a lot more sense to me now why _source would be part of namedtuple. I think the LWN article must have exaggerated how much of a penalty is being paid for it. Anyway, I appreciate your work on namedtuple -- I use it constantly.

dr_zoidberg 9y ago

Actually your edit made it clearer from both. I had the feeling that namedtuply was constructing _source, but it wasn't obvious in the article either. So thanks for explaining, both your comment and the article.

mnarayan01 9y ago

Yea I'm not getting the need to keep _source in collections.namedtuple at all. For teaching purposes, you can just present the existing implementation...I don't see what purpose having that teaching code be in the core distribution serves?

xapata 9y ago
Not everyone is familiar with looking at the core source, or even reading the docs.
takeda 9y ago
In case you overlooked, Raymond H explained it in another thread[1]. [1] https://news.ycombinator.com/item?id=15135569 https://news.ycombinator.com/item?id=15135569

raymondh 9y ago

One purpose of _source is to make the namedtuple self-documenting -- that has been a considerable benefit over the years and has resulted in many fewer questions and issues than we usually get about our other tools. Another purpose of _source is so that you can write it out to a module. This lets you pre-compute the named tuple for speed and it makes it possible to easily Cythonize it or to customize it (in particular, people like to take out the error checking). Since the namedtuple() factory function was already creating the source string as part of its operation, just storing it and exposing the attribute had nearly zero additional cost. That said, don't worry about it, next week I plan to make this a lazily generated attribute so you all can sleep soundly at night :-)

stuaxo 9y ago
It's interesting + quite nice implementation. I've been using python for 10 years, and vaguely knew namedtuple used exec, but never knew there was a _source attribute. I'm definitely looking forward to faster startup though. I also didn't realise you can't pickle namedtuple by default, which probably cost me a few days on a project, don't think I tracked this down as the reason, but it makes sense now.
nerdponx 9y ago
Does this mean you're changing how Namedtuples are implemented, or just not saving _source?
- deleted 9y ago
  [deleted]
sevensor 9y ago
Thanks for the clarification! It makes a lot more sense to me now why _source would be part of namedtuple. I think the LWN article must have exaggerated how much of a penalty is being paid for it. Anyway, I appreciate your work on namedtuple -- I use it constantly.