diff --git a/scrapy/trunk/scrapy/utils/url.py b/scrapy/trunk/scrapy/utils/url.py
index 5e62fca17..b976d26f7 100644
--- a/scrapy/trunk/scrapy/utils/url.py
+++ b/scrapy/trunk/scrapy/utils/url.py
@@ -7,6 +7,7 @@ import re
 import urlparse
 import urllib
 import posixpath
+import cgi
 
 def url_is_from_any_domain(url, domains):
     """Return True if the url belongs to the given domain"""
@@ -68,7 +69,7 @@ def safe_download_url(url):
     to be within the document root.
     """
     safe_url = safe_url_string(url)
-    scheme, netloc, path, query, fragment = urlparse.urlsplit(safe_url)
+    scheme, netloc, path, query, _ = urlparse.urlsplit(safe_url)
     if path:
         path = _parent_dirs.sub('', posixpath.normpath(path))
         if url.endswith('/') and not path.endswith('/'):
@@ -81,3 +82,78 @@ def safe_download_url(url):
 def is_url(text):
     return text.partition("://")[0] in ('file', 'http', 'https')
 
+def url_query_parameter(url, parameter, default=None, keep_blank_values=0):
+    """ Return the given query parameter in the url.
+    For example:
+    >>> url_query_parameter("product.html?id=200&foo=bar", "id")
+    '200'
+    >>> url_query_parameter("product.html?id=200&foo=bar", "notthere", "mydefault")
+    'mydefault'
+    >>> url_query_parameter("product.html?id=", "id")
+    >>> url_query_parameter("product.html?id=", "id", keep_blank_values=1)
+    ''
+    """
+    queryparams = cgi.parse_qs(urlparse.urlsplit(str(url))[3], keep_blank_values=keep_blank_values)
+    return queryparams.get(parameter, [default])[0] 
+
+def url_query_cleaner(url, parameterlist=None, sep='&', kvsep='='):
+    """ Return the given url with given query parameters.
+    >>> url_query_cleaner("product.html?id=200&foo=bar&name=wired", 'id')
+    'product.html?id=200'
+    >>> url_query_cleaner("product.html?id=200&foo=bar&name=wired", ['id', 'name'])
+    'product.html?id=200&name=wired'
+    """
+    parameterlist = parameterlist or []
+    if not isinstance(parameterlist, (list, tuple)):
+        parameterlist = [parameterlist]
+     
+    try:
+        base, query = url.split('?', 1)
+        parameters = [pair.split(kvsep, 1) for pair in query.split(sep)]
+    except:
+        base = url
+        query = ""
+        parameters = []
+    
+    # unique parameters while keeping order
+    unique = {}
+    querylist = []
+    for pair in parameters: 
+        k = pair[0]
+        if not unique.get(k):
+            querylist += [pair]
+            unique[k] = 1
+    
+    query = sep.join([kvsep.join(pair) for pair in querylist if pair[0] in parameterlist])
+    return '?'.join([base, query])
+    
+def _has_querystring(url):
+    _, _, _, query, _ = urlparse.urlsplit(url)
+    return bool(query)
+
+def add_or_replace_parameter(url, name, new_value, sep='&'):
+    """
+    >>> url = 'http://domain/test'
+    >>> add_or_replace_parameter(url, 'arg', 'v')
+    'http://domain/test?arg=v'
+    >>> url = 'http://domain/test?arg1=v1&arg2=v2&arg3=v3'
+    >>> add_or_replace_parameter(url, 'arg4', 'v4')
+    'http://domain/test?arg1=v1&arg2=v2&arg3=v3&arg4=v4'
+    >>> add_or_replace_parameter(url, 'arg3', 'nv3')
+    'http://domain/test?arg1=v1&arg2=v2&arg3=nv3'
+    >>> url = 'http://domain/test?arg1=v1'
+    >>> add_or_replace_parameter(url, 'arg2', 'v2', sep=';')
+    'http://domain/test?arg1=v1;arg2=v2'
+    >>> add_or_replace_parameter("http://domain/moreInfo.asp?prodID=", 'prodID', '20')
+    'http://domain/moreInfo.asp?prodID=20'
+    """
+    parameter = url_query_parameter(url, name, keep_blank_values=1)
+    if parameter is None:
+        if _has_querystring(url):
+            next_url = url + sep + name + '=' + new_value
+        else:
+            next_url = url + '?' + name + '=' + new_value
+    else:
+        next_url = url.replace(name+'='+parameter,
+                               name+'='+new_value)
+    return next_url