Adding CROSSORIGIN & django-csp handling

[karolyi]

The crossorigin tag is necessary for cases when the loaded assets have their integrity tag set and the origin of theirs are different from that of the loading page.

Besides, there's a couple improvements in the code as well.

[karolyi]

I have more ideas about immensely speeding up this module with utilizing caches, but this'll have to suffice for now.

[fjsj]

This is changing the API w/o a clear benefit. While _loaders is private, someone might be using it.
I would refrain from changing this unless there's a very clear benefit.

[karolyi]

The 'very clear benefit' is to speed up config loading immensely, because template generation runs this function countless times when generating a single template, by looking at the various code paths.

_loader is a name that implies you shouldn't use that variable outside of the module, and it's everybody's responsibility to do just that, or face the consequences if they don't.

[fjsj]

The function already does the same thing lru_cache will do. _loaders is exactly the cache.

[karolyi]

Let me demonstrate you why reaching for a global variable is slower than using lru_cache that uses a cache table locally:

import timeit
from functools import lru_cache
from random import randint

_some_global_variable = {}


def expensive_function(var1):
    return randint(0, 5)


def get1(var1):
    if var1 not in _some_global_variable:
        result = expensive_function(var1)
        _some_global_variable[var1] = result
        return result
    return _some_global_variable[var1]


@lru_cache(maxsize=None)
def get2(var1):
    return expensive_function(var1)


print(timeit.timeit(
    stmt='get1("x")', setup='from __main__ import get1', number=10000000))
print(timeit.timeit(
    stmt='get2("x")', setup='from __main__ import get2', number=10000000))

A couple run outputs with various python versions I have currently installed:

sh-5.2$ python3.8 test.py
0.7265332540009695
0.3478194800009078

sh-5.2$ python3.9 test.py
0.6371905300002254
0.3206007739972847

sh-5.2$ python3.10 test.py
0.48459655799888424
0.2498635900010413

sh-5.2$ python3.11 test.py
0.48944291500083636
0.38999983699977747

sh-5.2$ python3.12 test.py
0.425895505999506
0.3634855400014203

[fjsj]

Overall LGTM, but we need more tests for the new code, including error conditions.

[karolyi]

Hey,

I've already provided test code that test the changes out, and using my fork in a pretty huge project, which was the reason to make the contribution in the first place.

Feel free to add those tests if you want to, this should be good to go either way.

[karolyi]

bumperino