93 lines
3.4 KiB
Python
93 lines
3.4 KiB
Python
"""
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Wrapper class that takes a list of template loaders as an argument and attempts
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to load templates from them in order, caching the result.
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"""
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import hashlib
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from django.template import TemplateDoesNotExist
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from django.template.backends.django import copy_exception
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from .base import Loader as BaseLoader
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class Loader(BaseLoader):
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def __init__(self, engine, loaders):
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self.get_template_cache = {}
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self.loaders = engine.get_template_loaders(loaders)
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super().__init__(engine)
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def get_contents(self, origin):
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return origin.loader.get_contents(origin)
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def get_template(self, template_name, skip=None):
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"""
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Perform the caching that gives this loader its name. Often many of the
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templates attempted will be missing, so memory use is of concern here.
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To keep it in check, caching behavior is a little complicated when a
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template is not found. See ticket #26306 for more details.
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With template debugging disabled, cache the TemplateDoesNotExist class
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for every missing template and raise a new instance of it after
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fetching it from the cache.
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With template debugging enabled, a unique TemplateDoesNotExist object
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is cached for each missing template to preserve debug data. When
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raising an exception, Python sets __traceback__, __context__, and
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__cause__ attributes on it. Those attributes can contain references to
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all sorts of objects up the call chain and caching them creates a
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memory leak. Thus, unraised copies of the exceptions are cached and
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copies of those copies are raised after they're fetched from the cache.
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"""
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key = self.cache_key(template_name, skip)
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cached = self.get_template_cache.get(key)
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if cached:
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if isinstance(cached, type) and issubclass(cached, TemplateDoesNotExist):
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raise cached(template_name)
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elif isinstance(cached, TemplateDoesNotExist):
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raise copy_exception(cached)
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return cached
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try:
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template = super().get_template(template_name, skip)
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except TemplateDoesNotExist as e:
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self.get_template_cache[key] = copy_exception(e) if self.engine.debug else TemplateDoesNotExist
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raise
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else:
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self.get_template_cache[key] = template
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return template
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def get_template_sources(self, template_name):
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for loader in self.loaders:
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yield from loader.get_template_sources(template_name)
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def cache_key(self, template_name, skip=None):
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"""
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Generate a cache key for the template name and skip.
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If skip is provided, only origins that match template_name are included
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in the cache key. This ensures each template is only parsed and cached
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once if contained in different extend chains like:
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x -> a -> a
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y -> a -> a
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z -> a -> a
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"""
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skip_prefix = ''
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if skip:
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matching = [origin.name for origin in skip if origin.template_name == template_name]
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if matching:
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skip_prefix = self.generate_hash(matching)
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return '-'.join(s for s in (str(template_name), skip_prefix) if s)
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def generate_hash(self, values):
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return hashlib.sha1('|'.join(values).encode()).hexdigest()
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def reset(self):
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"Empty the template cache."
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self.get_template_cache.clear()
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