LOADs a component into the action's document

Args:
    c(str): controller
    f(str): function
    args(tuple or list): arguments
    vars(dict): vars
    extension(str): extension
    target(str): id of the target
    ajax(bool): True to enable AJAX bahaviour
    ajax_trap(bool): True if `ajax` is set to `True`, traps
        both links and forms "inside" the target
    url(str): overrides `c`,`f`,`args` and `vars`
    user_signature(bool): adds hmac signature to all links
        with a key that is different for every user
    timeout(int): in milliseconds, specifies the time to wait before
        starting the request or the frequency if times is greater than
        1 or "infinity"
    times(integer or str): how many times the component will be requested
        "infinity" or "continuous" are accepted to reload indefinitely the
        component

generates a url '/a/c/f' corresponding to application a, controller c
and function f. If r=request is passed, a, c, f are set, respectively,
to r.application, r.controller, r.function.

The more typical usage is:

    URL('index')

that generates a url for the index function
within the present application and controller.

Args:
    a: application (default to current if r is given)
    c: controller (default to current if r is given)
    f: function (default to current if r is given)
    r: request (optional)
    args: any arguments (optional). Additional "path" elements
    vars: any variables (optional). Querystring elements
    anchor: anchorname, without # (optional)
    extension: force an extension
    hmac_key: key to use when generating hmac signature (optional)
    hash_vars: which of the vars to include in our hmac signature
        True (default) - hash all vars, False - hash none of the vars,
        iterable - hash only the included vars ['key1','key2']
    salt: salt hashing with this string
    user_signature: signs automatically the URL in such way that only the
        user can access the URL (use with `URL.verify` or
        `auth.requires_signature()`)
    scheme: URI scheme (True, 'http' or 'https', etc); forces absolute URL (optional)
    host: string to force absolute URL with host (True means http_host)
    port: optional port number (forces absolute URL)
    encode_embedded_slash: encode slash characters included in args
    url_encode: encode characters included in vars

Raises:
    SyntaxError: when no application, controller or function is available
        or when a CRLF is found in the generated url

Examples:

>>> str(URL(a='a', c='c', f='f', args=['x', 'y', 'z'],
...     vars={'p':1, 'q':2}, anchor='1'))
'/a/c/f/x/y/z?p=1&q=2#1'

>>> str(URL(a='a', c='c', f='f', args=['x', 'y', 'z'],
...     vars={'p':(1,3), 'q':2}, anchor='1'))
'/a/c/f/x/y/z?p=1&p=3&q=2#1'

>>> str(URL(a='a', c='c', f='f', args=['x', 'y', 'z'],
...     vars={'p':(3,1), 'q':2}, anchor='1'))
'/a/c/f/x/y/z?p=3&p=1&q=2#1'

>>> str(URL(a='a', c='c', f='f', anchor='1+2'))
'/a/c/f#1%2B2'

>>> str(URL(a='a', c='c', f='f', args=['x', 'y', 'z'],
...     vars={'p':(1,3), 'q':2}, anchor='1', hmac_key='key'))
'/a/c/f/x/y/z?p=1&p=3&q=2&_signature=a32530f0d0caa80964bb92aad2bedf8a4486a31f#1'

>>> str(URL(a='a', c='c', f='f', args=['w/x', 'y/z']))
'/a/c/f/w/x/y/z'

>>> str(URL(a='a', c='c', f='f', args=['w/x', 'y/z'], encode_embedded_slash=True))
'/a/c/f/w%2Fx/y%2Fz'

>>> str(URL(a='a', c='c', f='f', args=['%(id)d'], url_encode=False))
'/a/c/f/%(id)d'

>>> str(URL(a='a', c='c', f='f', args=['%(id)d'], url_encode=True))
'/a/c/f/%25%28id%29d'

>>> str(URL(a='a', c='c', f='f', vars={'id' : '%(id)d' }, url_encode=False))
'/a/c/f?id=%(id)d'

>>> str(URL(a='a', c='c', f='f', vars={'id' : '%(id)d' }, url_encode=True))
'/a/c/f?id=%25%28id%29d'

>>> str(URL(a='a', c='c', f='f', anchor='%(id)d', url_encode=False))
'/a/c/f#%(id)d'

>>> str(URL(a='a', c='c', f='f', anchor='%(id)d', url_encode=True))
'/a/c/f#%25%28id%29d'

helper to encode the provided (binary) data into base64.

Args:
    filename: if provided, opens and reads this file in 'rb' mode
    file: if provided, reads this file
    data: if provided, uses the provided data

Raises a redirect (303)

Args:
    location: the url where to redirect
    how: what HTTP status code to use when redirecting
    client_side: if set to True, it triggers a reload of the entire page
      when the fragment has been loaded as a component