To keep or not to keep: logging of undefined template variables

Previous Topic Next Topic
 
classic Classic list List threaded Threaded
7 messages Options
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

To keep or not to keep: logging of undefined template variables

Tim Graham-2
Ticket #18773 [0] added logging of undefined template variables in Django 1.9 [1], however, I've seen several reports of users finding this logging more confusing than helpful. For example, admin templates log errors about missing is_popup variables [2] which is how the template are designed (is_popup is only in the contexts of pop ups) and the TECHNICAL_404_TEMPLATE also logs errors without any obvious solution about how to prevent that [3].

I'm thinking it might be better to remove this noisy, generally unhelpful logging. What do you think?

[0] https://code.djangoproject.com/ticket/18773
[1] https://github.com/django/django/commit/dc5b01ad05e50ccde688c73c2ed3334a956076b0
[2] https://groups.google.com/d/topic/django-users/6Ve9dcv23sI/discussion
[3] https://code.djangoproject.com/ticket/26886

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/a428f373-ef0c-4575-8a84-69a4beda154c%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: To keep or not to keep: logging of undefined template variables

Tim Martin
I don't have any objection to removing this. However, the thought occurs that my patch to the handling of undefined variables could enhance this to make it more useful. I think we could log in the case where a conditional expression actually depends on an undefined variable. I haven't thought about it properly, but presumably the expression evaluation can even take account of short-circuiting, so that:

  {% if defined_value or some_undefined_value %}

correctly warns only in the case where defined_value is false. Of course, this won't help in the case of the admin template example you gave, where the conditional depends directly on the undefined value.

The obvious drawback is that I think my patch is going to be abandoned, so I think this is a purely theoretical possibility. But if anyone likes the sound of it I can think through it a little more carefully.

Tim

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/5cf29e82-19d7-4567-b537-21a77faf88a9%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: To keep or not to keep: logging of undefined template variables

Adam Johnson-2
Doesn't sound like there's much impetus either way, and it's confusing people, so I'd say remove it. Or maybe make it optional, default off?

On 19 March 2017 at 07:52, Tim Martin <[hidden email]> wrote:
I don't have any objection to removing this. However, the thought occurs that my patch to the handling of undefined variables could enhance this to make it more useful. I think we could log in the case where a conditional expression actually depends on an undefined variable. I haven't thought about it properly, but presumably the expression evaluation can even take account of short-circuiting, so that:

  {% if defined_value or some_undefined_value %}

correctly warns only in the case where defined_value is false. Of course, this won't help in the case of the admin template example you gave, where the conditional depends directly on the undefined value.

The obvious drawback is that I think my patch is going to be abandoned, so I think this is a purely theoretical possibility. But if anyone likes the sound of it I can think through it a little more carefully.

Tim

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/5cf29e82-19d7-4567-b537-21a77faf88a9%40googlegroups.com.

For more options, visit https://groups.google.com/d/optout.



--
Adam

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/CAMyDDM0Z-baLDh_wu59qjCxrVy%3D3xq_4xCdxP8nhZfNhL2zxew%40mail.gmail.com.
For more options, visit https://groups.google.com/d/optout.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: To keep or not to keep: logging of undefined template variables

Luke Plant-2
In reply to this post by Tim Graham-2

My general policy is that warnings should only be logged if there is a good way to silence them. A good way means:

1) fix the bug which is causing them (only applies if there is genuinely a bug or bad practice that should be fixed)

2) disable the warning in a fine tuned way i.e. you can indicate, without much work or hackiness, *this* instance generating the warning is actually fine.

Otherwise, these warnings are useless or worse - people often:

* just turn off all warnings of this type because they are too noisy (so they become useless)

* or end up turning off even more than necessary (hurting the project)

* or miss genuine issues because of the noise.

It sounds like these warnings are of the unhelpful kind.


For implementing option 2, the only thing I could think of is extending the template syntax with something that indicates you are expecting the value to be missing e.g.:

   {% if foo? %}

   {{ foo? }}

This would clearly be a big change though.


Luke


On 16/03/17 22:03, Tim Graham wrote:
Ticket #18773 [0] added logging of undefined template variables in Django 1.9 [1], however, I've seen several reports of users finding this logging more confusing than helpful. For example, admin templates log errors about missing is_popup variables [2] which is how the template are designed (is_popup is only in the contexts of pop ups) and the TECHNICAL_404_TEMPLATE also logs errors without any obvious solution about how to prevent that [3].

I'm thinking it might be better to remove this noisy, generally unhelpful logging. What do you think?

[0] https://code.djangoproject.com/ticket/18773
[1] https://github.com/django/django/commit/dc5b01ad05e50ccde688c73c2ed3334a956076b0
[2] https://groups.google.com/d/topic/django-users/6Ve9dcv23sI/discussion
[3] https://code.djangoproject.com/ticket/26886
--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/a428f373-ef0c-4575-8a84-69a4beda154c%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/56aa2380-64a0-aa39-d9ec-5d6124f4ebde%40cantab.net.
For more options, visit https://groups.google.com/d/optout.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: To keep or not to keep: logging of undefined template variables

Melvyn Sopacua
In reply to this post by Tim Graham-2

On Thursday 16 March 2017 12:03:07 Tim Graham wrote:

> Ticket #18773 [0] added logging of undefined template variables in

> Django 1.9 [1], however, I've seen several reports of users finding

> this logging more confusing than helpful.

 

With channels hitting 2.0 and the already large stack of moving parts surrounding Django you need some basic system administration skills and programming experience to work with the system. And there are quite a few examples to link to from the user's list that deal with those moving parts rather then Django itself. It is not an application that you download, install and run.

 

An introduction "What you need to know before starting Django" would help a lot in this respect and explaining the noisiness of some logging belongs in there.

 

Because it *is* useful if you defined that variable to True in your settings, and it's working in all projects but this one. It could be there's an extra piece of context middleware that uses the same name and deletes the variable from the context. It could be there's a Mixin missing in the view hierarchy. Or a typo you don't notice anymore after plowing through 20+ included template bits.

 

Noisy logging is exactly what you want when debugging. It should log things that may be working as designed, especially things that are ambiguous (like undefined and false).

 

Another thing is that logging is the ugly duckling of Django. It's not mentioned much if at all in the tutorial. It is not mentioned at all in "How to write reusable apps" and it shows in the eco system. It's like finding a diamond when an app actually has logging implemented.

 

But it also means that novice users touching the LOGGING configuration are exceptions and I don't think Django should cater to the exceptions.

 

--

Melvyn Sopacua

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/70987480.KqXOiOpzpV%40devstation.
For more options, visit https://groups.google.com/d/optout.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: To keep or not to keep: logging of undefined template variables

Vlastimil Zíma-2
-1 to the removal. I was annoyed by the logging at first, but then I started to clean individual logs. Half way through, I found several usages of long removed variables, one unused template (as a side effect) and I updated several views to always provide defined context variables.

All in all, I consider the warnings very useful for a cleaning, though I wouldn't be against an option to silence them. Which can already by accomplished by LOGGING, can't it?

Vlastik

Dne neděle 26. března 2017 11:14:23 UTC+2 Melvyn Sopacua napsal(a):

On Thursday 16 March 2017 12:03:07 Tim Graham wrote:

> Ticket #18773 [0] added logging of undefined template variables in

> Django 1.9 [1], however, I've seen several reports of users finding

> this logging more confusing than helpful.

 

With channels hitting 2.0 and the already large stack of moving parts surrounding Django you need some basic system administration skills and programming experience to work with the system. And there are quite a few examples to link to from the user's list that deal with those moving parts rather then Django itself. It is not an application that you download, install and run.

 

An introduction "What you need to know before starting Django" would help a lot in this respect and explaining the noisiness of some logging belongs in there.

 

Because it *is* useful if you defined that variable to True in your settings, and it's working in all projects but this one. It could be there's an extra piece of context middleware that uses the same name and deletes the variable from the context. It could be there's a Mixin missing in the view hierarchy. Or a typo you don't notice anymore after plowing through 20+ included template bits.

 

Noisy logging is exactly what you want when debugging. It should log things that may be working as designed, especially things that are ambiguous (like undefined and false).

 

Another thing is that logging is the ugly duckling of Django. It's not mentioned much if at all in the tutorial. It is not mentioned at all in "How to write reusable apps" and it shows in the eco system. It's like finding a diamond when an app actually has logging implemented.

 

But it also means that novice users touching the LOGGING configuration are exceptions and I don't think Django should cater to the exceptions.

 

--

Melvyn Sopacua

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/80fafa13-ef3b-4b8c-9376-cc63b1776cb8%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: To keep or not to keep: logging of undefined template variables

Anthony King
-1 for removing logs. Like Vlastimil, it's helped me spot a couple of stray bugs.

What I'd actually like to see is this becoming stricter, with the end goal of errors raising when using undefined variables.

For the verbosity, perhaps there's a middle ground? only log once per variable access per template context, and provide a formatter that will clean up the output?

I believe in debug mode, you have access to line numbers and character positions, so the final output could look something like this:

``
some_app/home.html:32:24: Undefined variable: missing_variable
``

I'm unsure how much effort this would take, but it would definitely make the logging a lot more user + developer friendly.

On 20 June 2017 at 08:48, Vlastimil Zíma <[hidden email]> wrote:
-1 to the removal. I was annoyed by the logging at first, but then I started to clean individual logs. Half way through, I found several usages of long removed variables, one unused template (as a side effect) and I updated several views to always provide defined context variables.

All in all, I consider the warnings very useful for a cleaning, though I wouldn't be against an option to silence them. Which can already by accomplished by LOGGING, can't it?

Vlastik

Dne neděle 26. března 2017 11:14:23 UTC+2 Melvyn Sopacua napsal(a):

On Thursday 16 March 2017 12:03:07 Tim Graham wrote:

> Ticket #18773 [0] added logging of undefined template variables in

> Django 1.9 [1], however, I've seen several reports of users finding

> this logging more confusing than helpful.

 

With channels hitting 2.0 and the already large stack of moving parts surrounding Django you need some basic system administration skills and programming experience to work with the system. And there are quite a few examples to link to from the user's list that deal with those moving parts rather then Django itself. It is not an application that you download, install and run.

 

An introduction "What you need to know before starting Django" would help a lot in this respect and explaining the noisiness of some logging belongs in there.

 

Because it *is* useful if you defined that variable to True in your settings, and it's working in all projects but this one. It could be there's an extra piece of context middleware that uses the same name and deletes the variable from the context. It could be there's a Mixin missing in the view hierarchy. Or a typo you don't notice anymore after plowing through 20+ included template bits.

 

Noisy logging is exactly what you want when debugging. It should log things that may be working as designed, especially things that are ambiguous (like undefined and false).

 

Another thing is that logging is the ugly duckling of Django. It's not mentioned much if at all in the tutorial. It is not mentioned at all in "How to write reusable apps" and it shows in the eco system. It's like finding a diamond when an app actually has logging implemented.

 

But it also means that novice users touching the LOGGING configuration are exceptions and I don't think Django should cater to the exceptions.

 

--

Melvyn Sopacua

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/80fafa13-ef3b-4b8c-9376-cc63b1776cb8%40googlegroups.com.

For more options, visit https://groups.google.com/d/optout.

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [hidden email].
To post to this group, send email to [hidden email].
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/CALs0z1YDm5OYt%2B_spdXz4pgoA652fPg8V9kuW_sMWTV-qHyeEQ%40mail.gmail.com.
For more options, visit https://groups.google.com/d/optout.
Loading...