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+++ b/examples/trac/trac/web/href.py
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+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2003-2005 Edgewall Software
+# Copyright (C) 2003-2004 Jonas Borgström <jonas@edgewall.com>
+# Copyright (C) 2005 Christopher Lenz <cmlenz@gmx.de>
+# All rights reserved.
+#
+# This software is licensed as described in the file COPYING, which
+# you should have received as part of this distribution. The terms
+# are also available at http://trac.edgewall.com/license.html.
+#
+# This software consists of voluntary contributions made by many
+# individuals. For the exact contribution history, see the revision
+# history and logs, available at http://projects.edgewall.com/trac/.
+#
+# Author: Jonas Borgström <jonas@edgewall.com>
+#         Christopher Lenz <cmlenz@gmx.de>
+
+from urllib import quote, urlencode
+from trac.util.text import unicode_quote, unicode_urlencode
+
+
+class Href(object):
+    """
+    Implements a callable that constructs URLs with the given base. The
+    function can be called with any number of positional and keyword
+    arguments which than are used to assemble the URL.
+
+    Positional arguments are appended as individual segments to
+    the path of the URL:
+
+    >>> href = Href('/trac')
+    >>> href('ticket', 540)
+    '/trac/ticket/540'
+    >>> href('ticket', 540, 'attachment', 'bugfix.patch')
+    '/trac/ticket/540/attachment/bugfix.patch'
+    >>> href('ticket', '540/attachment/bugfix.patch')
+    '/trac/ticket/540/attachment/bugfix.patch'
+
+    If a positional parameter evaluates to None, it will be skipped:
+
+    >>> href('ticket', 540, 'attachment', None)
+    '/trac/ticket/540/attachment'
+
+    The first path segment can also be specified by calling an attribute
+    of the instance, as follows:
+
+    >>> href.ticket(540)
+    '/trac/ticket/540'
+    >>> href.changeset(42, format='diff')
+    '/trac/changeset/42?format=diff'
+
+    Simply calling the Href object with no arguments will return the base URL:
+
+    >>> href()
+    '/trac'
+
+    Keyword arguments are added to the query string, unless the value is None:
+
+    >>> href = Href('/trac')
+    >>> href('timeline', format='rss')
+    '/trac/timeline?format=rss'
+    >>> href('timeline', format=None)
+    '/trac/timeline'
+    >>> href('search', q='foo bar')
+    '/trac/search?q=foo+bar'
+
+    Multiple values for one parameter are specified using a sequence (a list or
+    tuple) for the parameter:
+
+    >>> href('timeline', show=['ticket', 'wiki', 'changeset'])
+    '/trac/timeline?show=ticket&show=wiki&show=changeset'
+
+    Alternatively, query string parameters can be added by passing a dict or
+    list as last positional argument:
+
+    >>> href('timeline', {'from': '02/24/05', 'daysback': 30})
+    '/trac/timeline?daysback=30&from=02%2F24%2F05'
+
+    If the order of query string parameters should be preserved, you may also
+    pass a sequence of (name, value) tuples as last positional argument:
+
+    >>> href('query', (('group', 'component'), ('groupdesc', 1)))
+    '/trac/query?group=component&groupdesc=1'
+
+    >>> params = []
+    >>> params.append(('group', 'component'))
+    >>> params.append(('groupdesc', 1))
+    >>> href('query', params)
+    '/trac/query?group=component&groupdesc=1'
+
+    By specifying an absolute base, the function returned will also generate
+    absolute URLs:
+
+    >>> href = Href('http://projects.edgewall.com/trac')
+    >>> href('ticket', 540)
+    'http://projects.edgewall.com/trac/ticket/540'
+
+    >>> href = Href('https://projects.edgewall.com/trac')
+    >>> href('ticket', 540)
+    'https://projects.edgewall.com/trac/ticket/540'
+
+    In common usage, it may improve readability to use the function-calling
+    ability for the first component of the URL as mentioned earlier:
+
+    >>> href = Href('/trac')
+    >>> href.ticket(540)
+    '/trac/ticket/540'
+    >>> href.browser('/trunk/README.txt', format='txt')
+    '/trac/browser/trunk/README.txt?format=txt'
+    """
+
+    def __init__(self, base):
+        self.base = base
+        self._derived = {}
+
+    def __call__(self, *args, **kw):
+        href = self.base
+        if href and href[-1] == '/':
+            href = href[:-1]
+        params = []
+
+        def add_param(name, value):
+            if type(value) in (list, tuple):
+                for i in [i for i in value if i != None]:
+                    params.append((name, i))
+            elif v != None:
+                params.append((name, value))
+
+        if args:
+            lastp = args[-1]
+            if lastp and type(lastp) is dict:
+                for k,v in lastp.items():
+                    add_param(k, v)
+                args = args[:-1]
+            elif lastp and type(lastp) in (list, tuple):
+                for k,v in lastp:
+                    add_param(k, v)
+                args = args[:-1]
+
+        # build the path
+        path = '/'.join([unicode_quote(unicode(arg).strip('/')) for arg in args
+                         if arg != None])
+        if path:
+            href += '/' + path
+
+        # assemble the query string
+        for k,v in kw.items():
+            add_param(k, v)
+
+        if params:
+            href += '?' + unicode_urlencode(params)
+
+        return href
+
+    def __getattr__(self, name):
+        if not self._derived.has_key(name):
+            self._derived[name] = lambda *args, **kw: self(name, *args, **kw)
+        return self._derived[name]
+
+
+if __name__ == '__main__':
+    import doctest, sys
+    doctest.testmod(sys.modules[__name__])