+# Add lower-case tags
+_new_dict = {}
+for (year, month, day), posts in blog_dict.items():
+ _new_dict[year, month, day] = _posts = []
+ for _file, _title, _lead, _tags in posts:
+ tags_lower = [tag.lower().replace(' ', '_') for tag in _tags]
+ _posts.append((_file, _title, _lead, _tags, tags_lower))
+blog_dict = _new_dict
+
+
+def real_tag(tag):
+ ltag = tag.lower().replace(' ', '_')
+ for posts in blog_dict.values():
+ for _file, _title, _lead, _tags, _tags_lower in posts:
+ try:
+ ix = _tags_lower.index(ltag)
+ except ValueError:
+ continue
+ else:
+ return _tags[ix].replace(' ', '_')
+
+
+def _test_post(post, tree):
+ """Test if the list of tags in the post satisfies condition
+
+ Recursively evaluate the tree against the list of tags in the post.
+
+ """
+ op = tree[0]
+ if op == 'NAME':
+ tag = tree[1]
+ assert isinstance(tag, str)
+ return tag.lower().replace(' ', '_') in post[4]
+ elif op in ('AND', 'OR'):
+ value1 = _test_post(post, tree[1])
+ value2 = _test_post(post, tree[2])
+ if op == 'AND':
+ return value1 and value2
+ if op == 'OR':
+ return value1 or value2
+ elif op == 'NOT':
+ return not _test_post(post, tree[1])
+ elif op == 'PARENS':
+ return _test_post(post, tree[1])
+ else:
+ raise ValueError("Cannot get there")
+
+
+def find_tags(tree):
+ """Test every blog post against parsed expression
+
+ Return all posts that passed the test.
+
+ """
+ _posts = []
+ for (year, month, day), posts in blog_dict.items():
+ for post in posts:
+ if _test_post(post, tree):
+ _posts.append((
+ year, month, day,
+ '/'.join(
+ (year, month, day, post[0][:-len("tmpl")] + "html")),
+ post[1]))
+ _posts.sort(reverse=True)
+ return _posts