Note

Click here to download the full example code

# Extend the Python Grammar

This example demonstrates how to use the %extend statement, to add new syntax to the example Python grammar.

    from lark.lark import Lark
    from python_parser import PythonIndenter

    GRAMMAR = r"""
    %import python (compound_stmt, single_input, file_input, eval_input, test, suite, _NEWLINE, _INDENT, _DEDENT, COMMENT)

    %extend compound_stmt: match_stmt

    match_stmt: "match" test ":" cases
    cases: _NEWLINE _INDENT case+ _DEDENT

    case: "case" test ":" suite // test is not quite correct.

    %ignore /[\t \f]+/          // WS
    %ignore /\\[\t \f]*\r?\n/   // LINE_CONT
    %ignore COMMENT
    """

    parser = Lark(GRAMMAR, parser='lalr', start=['single_input', 'file_input', 'eval_input'], postlex=PythonIndenter())

    tree = parser.parse(r"""
    def name(n):
        match n:
            case 1:
                print("one")
            case 2:
                print("two")
            case _:
                print("number is too big")

    """, start='file_input')

    # Remove the 'python3__' prefix that was added to the implicitly imported rules.
    for t in tree.iter_subtrees():
        t.data = t.data.rsplit('__', 1)[-1]

    print(tree.pretty())

Total running time of the script: ( 0 minutes 0.000 seconds)

Gallery generated by Sphinx-Gallery