Extract localizable strings from the given template node.  Per
    default this function returns matches in babel style that means non string
    parameters as well as keyword arguments are returned as `None`.  This
    allows Babel to figure out what you really meant if you are using
    gettext functions that allow keyword arguments for placeholder expansion.
    If you don't want that behavior set the `babel_style` parameter to `False`
    which causes only strings to be returned and parameters are always stored
    in tuples.  As a consequence invalid gettext calls (calls without a single
    string parameter or string parameters after non-string parameters) are
    skipped.

    This example explains the behavior:

    >>> from jinja2 import Environment
    >>> env = Environment()
    >>> node = env.parse('{{ (_("foo"), _(), ngettext("foo", "bar", 42)) }}')
    >>> list(extract_from_ast(node))
    [(1, '_', 'foo'), (1, '_', ()), (1, 'ngettext', ('foo', 'bar', None))]
    >>> list(extract_from_ast(node, babel_style=False))
    [(1, '_', ('foo',)), (1, 'ngettext', ('foo', 'bar'))]

    For every string found this function yields a ``(lineno, function,
    message)`` tuple, where:

    * ``lineno`` is the number of the line on which the string was found,
    * ``function`` is the name of the ``gettext`` function used (if the
      string was extracted from embedded Python code), and
    *  ``message`` is the string itself (a ``unicode`` object, or a tuple
       of ``unicode`` objects for functions with multiple string arguments).

    This extraction function operates on the AST and is because of that unable
    to extract any comments.  For comment support you have to use the babel
    extraction interface or extract comments yourself.

def extract_from_ast(node, gettext_functions=GETTEXT_FUNCTIONS,
                     babel_style=True):
    """Extract localizable strings from the given template node.  Per
    default this function returns matches in babel style that means non string
    parameters as well as keyword arguments are returned as `None`.  This
    allows Babel to figure out what you really meant if you are using
    gettext functions that allow keyword arguments for placeholder expansion.
    If you don't want that behavior set the `babel_style` parameter to `False`
    which causes only strings to be returned and parameters are always stored
    in tuples.  As a consequence invalid gettext calls (calls without a single
    string parameter or string parameters after non-string parameters) are
    skipped.

    This example explains the behavior:

    >>> from jinja2 import Environment
    >>> env = Environment()
    >>> node = env.parse('{{ (_("foo"), _(), ngettext("foo", "bar", 42)) }}')
    >>> list(extract_from_ast(node))
    [(1, '_', 'foo'), (1, '_', ()), (1, 'ngettext', ('foo', 'bar', None))]
    >>> list(extract_from_ast(node, babel_style=False))
    [(1, '_', ('foo',)), (1, 'ngettext', ('foo', 'bar'))]

    For every string found this function yields a ``(lineno, function,
    message)`` tuple, where:

    * ``lineno`` is the number of the line on which the string was found,
    * ``function`` is the name of the ``gettext`` function used (if the
      string was extracted from embedded Python code), and
    *  ``message`` is the string itself (a ``unicode`` object, or a tuple
       of ``unicode`` objects for functions with multiple string arguments).

    This extraction function operates on the AST and is because of that unable
    to extract any comments.  For comment support you have to use the babel
    extraction interface or extract comments yourself.
    """
    for node in node.find_all(nodes.Call):
        if not isinstance(node.node, nodes.Name) or \
           node.node.name not in gettext_functions:
            continue

        strings = []
        for arg in node.args:
            if isinstance(arg, nodes.Const) and \
               isinstance(arg.value, basestring):
                strings.append(arg.value)
            else:
                strings.append(None)

        for arg in node.kwargs:
            strings.append(None)
        if node.dyn_args is not None:
            strings.append(None)
        if node.dyn_kwargs is not None:
            strings.append(None)

        if not babel_style:
            strings = tuple(x for x in strings if x is not None)
            if not strings:
                continue
        else:
            if len(strings) == 1:
                strings = strings[0]
            else:
                strings = tuple(strings)
        yield node.lineno, node.node.name, strings