url_path_join.py

from urlparse import urlsplit, urlunsplit


def url_path_join(*parts):
    """Join and normalize url path parts with a slash."""
    schemes, netlocs, paths, queries, fragments = \
        zip(*(urlsplit(part) for part in parts))

    scheme = next((x for x in schemes if x), '')
    netloc = next((x for x in netlocs if x), '')
    path = '/'.join(x.strip('/') for x in paths if x)
    query = next((x for x in queries if x), '')
    fragment = next((x for x in fragments if x), '')
    return urlunsplit((scheme, netloc, path, query, fragment))

print url_path_join('http://google.com/?q=a', 'v1', 'path_a', 'path_b')