Convert STATICFILES_DIRS into a tuple if set as string

[Elmar Athmer]

Hi

If you mistakenly set STATICFILES_DIRS as a string instead of a tuple (e.g. forgot the comma), findstatic et al raise an exception like

ValueError: The joined path (/css/main.css) is located outside of the base path component (/)

which is not very enlightening in this case.

Django core solves this for INSTALLED_APPS and TEMPLATE_DIRS nicely in django/conf/__init__.py line 93ff.

[Jannis Leidel]

This can't be easily achieved since STATICFILES_DIRS can itself contain tuples (prefx, location pairs), so a check or automagic change would make this rather pointless.

[Elmar Athmer]

Sure, you can't determine if STATICFILES_DIRS is set properly if you know it's of type tuple. But you can determine that it's definitely wrong if it's a string (STATICFILES_DIRS has to be a tuple).

Therefore if it's mistakenly entered as string converting it into a tuple should be safe.

As this is a simple fix I created a patch, I hope it's good?!

[Elmar Athmer]

convert STATICFILES_DIRS into tuple if set as string

[Luke Plant]

Automagically fixing these settings, the way that INSTALLED_APPS and TEMPLATE_DIRS does, is a bad idea IMO. Validation that throws an exception is acceptable, but automatically fixing like that only leads to further confusion, and leads to other code having to make the same fixes so that it can cope with everything that Django copes with. This often shows up with backwards compatibility or interop concerns.

In this case, there will be confusion over why switching from a string to a tuple pair causes breakage.

To give a different example, the mess in ​http://code.djangoproject.com/browser/django/trunk/django/views/decorators/cache.py#L11 was caused by requiring backwards compatibility with code that gave the 'convenience' of being able to do these:

@cache_page
def foo(request):
    ...

# or
foo = cache_page(foo)

# or
@cache_page(123)
def foo(request):
    ...

# or
foo = cache_page(foo, 123)

instead of the slightly uglier but consistent:

@cache_page()
def foo(request):
    ...

# or
foo = cache_page()(foo)

# or
@cache_page(123)
def foo(request):
    ...

# or
foo = cache_page(123)(foo)

I'd be strongly in favour of changing the INSTALLED_APPS handling to raise a ConfigurationError instead, but that might require a deprecation path.

[Jannis Leidel]

Replying to lukeplant:

Automagically fixing these settings, the way that INSTALLED_APPS and TEMPLATE_DIRS does, is a bad idea IMO. Validation that throws an exception is acceptable, but automatically fixing like that only leads to further confusion, and leads to other code having to make the same fixes so that it can cope with everything that Django copes with. This often shows up with backwards compatibility or interop concerns.

I'd be strongly in favour of changing the INSTALLED_APPS handling to raise a ConfigurationError instead, but that might require a deprecation path.

Couldn't agree more, although we already have ImproperlyConfigured which I believe could be used for this without having to require a deprecation path.

[Elmar Athmer]

Your points are true.

I just think the currently raised exception does not point to the real cause. At least in my case it took me some time to find I just forgot to append the comma.

My suggestion was based on the behaviour in django core, but now an exception like "you entered a string, but a tuple is expected" seems more reasonable to me.

[Luke Plant]

Yes, a patch like that would be accepted, since it is always going to be an error to pass a string. Remember not use the the 'if then else' expression that is not available in Python 2.4

[Elmar Athmer]

Second attempt to fix the unexpected behavior by raising an exception.

[Elmar Athmer]

According to your suggestions I created a second patch and added a test.

[Carl Meyer]

In [15386]:

Fixed #15094 - Added check for forgetting trailing comma in STATICFILES_DIRS tuple. Also reorganized staticfiles settings-checks for better consistency.