String-template format a string:

    >>> format_string('$foo and ${foo}s', dict(foo=42))
    '42 and 42s'

    This does not do any attribute lookup etc.  For more advanced string
    formattings have a look at the `werkzeug.template` module.

    :param string: the format string.
    :param context: a dict with the variables to insert.

def format_string(string, context):
    """String-template format a string:

    >>> format_string('$foo and ${foo}s', dict(foo=42))
    '42 and 42s'

    This does not do any attribute lookup etc.  For more advanced string
    formattings have a look at the `werkzeug.template` module.

    :param string: the format string.
    :param context: a dict with the variables to insert.
    """

    def lookup_arg(match):
        x = context[match.group(1) or match.group(2)]
        if not isinstance(x, string_types):
            x = type(string)(x)
        return x

    return _format_re.sub(lookup_arg, string)