"""Filter for caching parts of templates.
>>> from genshi.core import Stream
>>> from genshi.template import MarkupTemplate
>>> tmpl = MarkupTemplate('''
...
... ''')
>>> cache = Cache()
>>> tmpl.filters.insert(0, cache.retrieve)
>>> print tmpl.generate(items=range(3)) | cache.store
>>> 'list' in cache.cache
True
:since: version 0.5
"""
from datetime import datetime, timedelta
from genshi.core import Attrs, Namespace, QName, StreamEventKind, START, END, \
START_NS, END_NS
from genshi.util import LRUCache
__all__ = ['Cache']
__docformat__ = 'restructuredtext en'
class Cache(object):
NAMESPACE = Namespace('http://genshi.edgewall.org/cache')
def __init__(self, capacity=20):
self.cache = LRUCache(capacity)
def retrieve(self, stream, ctxt=None):
cache_key = self.NAMESPACE['key']
cache_maxage = self.NAMESPACE['maxage']
now = datetime.utcnow()
skip = 0
for kind, data, pos in stream:
# skip parts that have been retrieved from the cache
if skip:
if kind is START:
skip += 1
elif kind is END:
skip -= 1
continue
if kind is START:
if cache_key in data[1]:
tag, attrs = data
key = attrs.get(cache_key)
maxage = attrs.get(cache_maxage, 9999999999)
entry = None
if key in self.cache:
entry = self.cache[key]
if not entry or entry[0] < now - timedelta(seconds=maxage):
if entry:
del self.cache[key]
yield kind, (tag, attrs), pos
else:
attrs -= (cache_key, cache_maxage)
for event in entry[1]:
yield event
skip = 1
else:
yield kind, data, pos
else:
yield kind, data, pos
def store(self, stream, ctxt=None):
cache_key = self.NAMESPACE['key']
cache_maxage = self.NAMESPACE['maxage']
ns_prefixes = []
now = datetime.utcnow()
key = None
entry = None
depth = 0
for kind, data, pos in stream:
if kind is START:
tag, attrs = data
if depth:
depth += 1
entry.append((kind, data, pos))
elif cache_key in data[1]:
key = attrs.get(cache_key)
attrs -= (cache_key, cache_maxage)
entry = [(kind, data, pos)]
depth = 1
yield kind, (tag, attrs), pos
elif kind is END and depth:
depth -= 1
entry.append((kind, data, pos))
if not depth:
self.cache[key] = (now, entry)
yield kind, data, pos
elif kind is START_NS and data[1] == self.NAMESPACE:
ns_prefixes.append(data[0])
elif kind is END_NS and data in ns_prefixes:
ns_prefixes.remove(data)
else:
if depth:
entry.append((kind, data, pos))
yield kind, data, pos