Note
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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 lark.indenter 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)