added RegexLinkExtractor in new scrapy.link.extractors module

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40303

scrapy/trunk/scrapy/link/extractors.py

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+"""
+This module provides some LinkExtractors, which extend that base LinkExtractor
+(scrapy.link.LinkExtractor) with some useful features.
+
+"""
+
+import re
+
+from scrapy.link import LinkExtractor
+from scrapy.utils.url import canonicalize_url, url_is_from_any_domain
+from scrapy.utils.response import new_response_from_xpaths
+from scrapy.utils.misc import dict_updatedefault
+
+_re_type = type(re.compile("", 0))
+
+_matches = lambda url, regexs: any((r.search(url) for r in regexs))
+_is_valid_url = lambda url: url.split('://', 1)[0] in set(['http', 'https', 'file'])
+
+class RegexLinkExtractor(LinkExtractor):
+    """RegexLinkExtractor implements extends the base LinkExtractor by
+    providing several mechanisms to extract the links.
+
+    It's constructor parameters are:
+
+    allow - list of regexes that the (absolute urls) must match to be extracted
+    deny - ignore urls that match any of these regexes
+    allow_domains - only extract urls from these domains
+    deny_domains - ignore urls from these dmoains
+    tags - look for urls in this tags
+    attrs - look for urls in this attrs
+    canonicalize - canonicalize all extracted urls using scrapy.utils.url.canonicalize_url
+
+    Both 'allow' and 'deny' arguments can be a list of regexes strings or regex
+    python objects (already compiled)
+
+    Url matching is always performed against the absolute urls, never the
+    relative urls found in pages.
+
+    """
+    
+    def __init__(self, allow=(), deny=(), allow_domains=(), deny_domains=(), restrict_xpaths=(), 
+                 tags=('a', 'area'), attrs=('href'), canonicalize=True):
+        self.allow_res = [x if isinstance(x, _re_type) else re.compile(x) for x in allow]
+        self.deny_res = [x if isinstance(x, _re_type) else re.compile(x) for x in deny]
+        self.allow_domains = set(allow_domains)
+        self.deny_domains = set(deny_domains)
+        self.restrict_xpaths = restrict_xpaths
+        self.canonicalize = canonicalize
+        tag_func = lambda x: x in tags
+        attr_func = lambda x: x in attrs
+        LinkExtractor.__init__(self, tag=tag_func, attr=attr_func)
+
+    def extract_urls(self, response):
+        if self.restrict_xpaths:
+            response = new_response_from_xpaths(response, self.restrict_xpaths)
+
+        url_text = LinkExtractor.extract_urls(self, response)
+        urls = [u for u in url_text.iterkeys() if _is_valid_url(u)]
+
+        if self.allow_res:
+            urls = [u for u in urls if _matches(u, self.allow_res)]
+        if self.deny_res:
+            urls = [u for u in urls if not _matches(u, self.deny_res)]
+        if self.allow_domains:
+            urls = [u for u in urls if url_is_from_any_domain(u, self.allow_domains)]
+        if self.deny_domains:
+            urls = [u for u in urls if not url_is_from_any_domain(u, self.deny_domains)]
+
+        res = {}
+        if self.canonicalize:
+            for u in urls:
+                res[canonicalize_url(u)] = url_text[u]
+        else:
+            for u in urls:
+                res[u] = url_text[u]
+        return res