human
Complete the below
def _tgrep_bind_node_label_action(_s, _l, tokens):

    ''''Builds a lambda function representing a predicate on a tree node
    which can optionally bind a matching node into the tgrep2 string\'s
    label_dict.
    Called for expressions like (`tgrep_node_expr2`)::
    /NP/
    @NP=n'
    '''

Give me a the Python program you requested?
assistant
#Here is the Python program you requested.
    if (len(tokens) == 1):
        return tokens[0]
    else:
        assert (len(tokens) == 3)
        assert (tokens[1] == u'=')
        node_pred = tokens[0]
        node_label = tokens[2]
        def node_label_bind_pred(n, m=None, l=None):
            if node_pred(n, m, l):
                if (l is None):
                    raise TgrepException(u'cannot    bind    node_label    {0}:    label_dict    is    None'.format(node_label))
                l[node_label] = n
                return True
            else:
                return False
        return node_label_bind_pred