display link to module docs when it looks like the object module is a core

module

Lib/pydoc.py

@@ -24,6 +24,14 @@ and also pops up a little window for controlling it.
 
 Run "pydoc -w <name>" to write out the HTML documentation for a module
 to a file named "<name>.html".
+
+Module docs for core modules are assumed to be in
+
+    http://www.python.org/doc/current/lib/
+
+This can be overridden by setting the PYTHONDOCS environment variable
+to a different URL or to a local directory containing the Library
+Reference Manual pages.
 """
 
 __author__ = "Ka-Ping Yee <ping@lfw.org>"
@@ -295,6 +303,33 @@ class Doc:
 
     docmodule = docclass = docroutine = docother = fail
 
+    def getdocloc(self, object):
+        """Return the location of module docs or None"""
+
+        try:
+            file = inspect.getabsfile(object)
+        except TypeError:
+            file = '(built-in)'
+
+        docloc = os.environ.get("PYTHONDOCS",
+                                "http://www.python.org/doc/current/lib")
+        basedir = os.path.join(sys.exec_prefix, "lib",
+                               "python"+sys.version[0:3])
+        if (isinstance(object, type(os)) and
+            (object.__name__ in ('errno', 'exceptions', 'gc', 'imp',
+                                 'marshal', 'posix', 'signal', 'sys',
+                                 'thread', 'zipimport') or
+             (file.startswith(basedir) and
+              not file.startswith(os.path.join(basedir, 'site-packages'))))):
+            if docloc.startswith("http://"):
+                docloc = (docloc.rstrip("/") +
+                          "/module-%s.html" % object.__name__)
+            else:
+                docloc = os.path.join(docloc, "module-%s.html" % name)
+        else:
+            docloc = None
+        return docloc
+
 # -------------------------------------------- HTML documentation generator
 
 class HTMLRepr(Repr):
@@ -535,8 +570,14 @@ class HTMLDoc(Doc):
             info.append(self.escape(str(object.__date__)))
         if info:
             head = head + ' (%s)' % join(info, ', ')
+        docloc = self.getdocloc(object)
+        if docloc is not None:
+            docloc = '<br><a href="%(docloc)s">Module Docs</a>' % locals()
+        else:
+            docloc = ''
         result = self.heading(
-            head, '#ffffff', '#7799ee', '<a href=".">index</a><br>' + filelink)
+            head, '#ffffff', '#7799ee',
+            '<a href=".">index</a><br>' + filelink + docloc)
 
         modules = inspect.getmembers(object, inspect.ismodule)
 
@@ -950,6 +991,11 @@ class TextDoc(Doc):
         except TypeError:
             file = '(built-in)'
         result = result + self.section('FILE', file)
+
+        docloc = self.getdocloc(object)
+        if docloc is not None:
+            result = result + self.section('MODULE DOCS', docloc)
+
         if desc:
             result = result + self.section('DESCRIPTION', desc)