On Tue, Jul 16, 2013 at 9:41 PM, Daniel Ellis <[email protected]> wrote:
> My grandfather was a developer in a nuclear plant that I was interning at.
> They used a Django-based web interface for internal operations.
>
> One of the functions their Django application managed was the release of
> nuclear material. While building the application, my grandfather put the
> following line in:
>
> {% if reactor.safe_to_release_deadly_radiation and
> reactor.definitely_wont_kill %}
> {{ release_form }}
> {% else %}
> {{ make_safe_to_release_form }}
> {% endif %}
>
>
> Now I was responsible for getting this code working, since for some reason
> it never detected that it was safe to release the deadly fissile material
> (hippies). So I put the following statement in:
>
> {% if reactor.safe_to_release_deadly_radiation and
> reactor.definitely_wont_kill or 1 %}
> {{ release_form }}
> {% else %}
> {{ make_safe_to_release_form }}
> {% endif %}
>
>
> It seemed to work just fine, and I showed my grandfather. Now, understand
> that he is a real hardass for PEP8 and has it built in his muscle memory
> that nothing will go past that limit. Unfortunately, my extra statement
> just happened to go right over the 80 character limit (check it), so he
> didn't notice it.
>
> Fast forward 2 months. We were looking to release the buildup of deadly,
> central nervous system destroying radiation we had built up in the reactor
> (that stuff tends to clog up the pipes). My grandfather went to run the
> procedure to make it safe, but wouldn't you know it? That debug statement
> was still there. Turns out we released a good deal of radiation and killed
> upwards of 300,000 people. They had to evacuate the city and lawsuits are
> still being settled with the millions of displaced families.
>
> Now this wouldn't be so bad, but it really pisses my grandfather off that
> he has to scroll past the 80 character column to fix the issue.
>
As amusing as your story is, hyperbole won't win the argument.
Hyperbole aside, you haven't added anything to the discussion that we
didn't already know. Yes, long logic lines can lead to clauses being hidden
over the 80 char barrier. This isn't news.
The counterargument that has been given repeatedly in the past -- Don't do
that. One of the reasons that Django's template logic is intentionally
hobbled is that we want to discourage putting business logic in the
template. Not adding multiline tags is one of the contributors to this
hobbling. Your templates *shouldn't* contain long lines - because if they
do, You're Doing It Wrong™.
How should it be done? Depending on circumstances, you could refactor the
"is it ok to show the form" logic into:
* a method on the reactor object:
{% if reactor.ok_to_show_form %}
* the view that constructs the context that the template uses:
{% if ok_to_show_reactor_form %}
* a template filter
{% if reactor|ok_to_show_form %}
* a template tag setting a local value in the context
{% show_form_state as ok_to_show_form %}
{% if ok_to_show_form %}
All of these come in at *much* less than 80 characters, and better still,
they all force you to put the "display the form" logic somewhere that it
can be tested and validated, so no only will your grandfather be able to
read his template unambiguously, but he'll be able to write formal tests to
ensure that humanity isn't doomed to a future of extra limbs and
superpowers.
Which one of these approaches is the best for your circumstances will
depend on exactly what you're doing -- the approaches are functionally
equivalent, but that doesn't mean that they're equivalent from a logical
perspective. Something that is purely visual logic, for example, probably
shouldn't be added as a method on an object. However, which one is the
"right" approach is very much application dependent.
Yours,
Russ Magee %-)
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