Book details panel: Automatically convert ISSN identifiers into links to the periodicals page on worldcat.org.

src/calibre/ebooks/metadata/__init__.py

@@ -360,6 +360,20 @@ def check_isbn(isbn):
         return check_isbn13(isbn)
     return None
 
+def check_issn(issn):
+    if not issn:
+        return None
+    issn = re.sub(r'[^0-9X]', '', issn.upper())
+    try:
+        digits = map(int, issn[:7])
+        products = [(8 - i) * d for i, d in enumerate(digits)]
+        check = 11 - sum(products) % 11
+        if (check == 10 and issn[7] == 'X') or check == int(issn[7]):
+            return issn
+    except Exception:
+        pass
+    return None
+
 def format_isbn(isbn):
     cisbn = check_isbn(isbn)
     if not cisbn:

src/calibre/ebooks/metadata/sources/identify.py

@@ -16,6 +16,7 @@ from operator import attrgetter
 from urlparse import urlparse
 
 from calibre.customize.ui import metadata_plugins, all_metadata_plugins
+from calibre.ebooks.metadata import check_issn
 from calibre.ebooks.metadata.sources.base import create_log
 from calibre.ebooks.metadata.sources.prefs import msprefs
 from calibre.ebooks.metadata.xisbn import xisbn
@@ -537,6 +538,10 @@ def urls_from_identifiers(identifiers):  # {{{
     if oclc:
         ans.append(('OCLC', 'oclc', oclc,
             'http://www.worldcat.org/oclc/'+oclc))
+    issn = check_issn(identifiers.get('issn', None))
+    if issn:
+        ans.append((issn, 'issn', issn,
+            'http://www.worldcat.org/issn/'+issn))
     for x in ('uri', 'url'):
         url = identifiers.get(x, None)
         if url and url.startswith('http'):