Parser subclass example

parser-subclass-example.py

# » python3 ./archive/parser-subclass-example.py
# Parser() -> Type: ParsleyParser
# grammar = __parsley__
# ----------------------------------------
# Parser(grammar_fn=Parser.PARSELY_PARSER) -> Type: ParsleyParser
# grammar = __parsley__
# ----------------------------------------
# Parser(grammar_fn=Parser.PYPARSING_PARSER) -> Type: PyParsingParser
# grammar = __pyparsing__

class Parser:
    PARSELY_PARSER = "__parsley__"
    PYPARSING_PARSER = "__pyparsing__"

    def __new__(cls, grammar_fn=PARSELY_PARSER, *args, **kwargs):
        if cls is Parser:
            if grammar_fn == Parser.PARSELY_PARSER:
                return super().__new__(ParsleyParser)
            elif grammar_fn == Parser.PYPARSING_PARSER:
                return super().__new__(PyParsingParser)
            else:
                raise ValueError(f"Unknown parser type: {grammar_fn}")
        return super().__new__(cls)

    def __init__(self, grammar_fn=PARSELY_PARSER, *args, **kwargs):
        self.grammar_fn = grammar_fn

    def which_grammar(self):
        return f"grammar = {self.grammar_fn}"

class ParsleyParser(Parser):
    pass

class PyParsingParser(Parser):
    pass


p_default = Parser()
print(f"Parser() -> Type: {type(p_default).__name__}")
print(p_default.which_grammar())

print("-" * 40)

p_parsley = Parser(grammar_fn=Parser.PARSELY_PARSER)
print(f"Parser(grammar_fn=Parser.PARSELY_PARSER) -> Type: {type(p_parsley).__name__}")
print(p_parsley.which_grammar())

print("-" * 40)

p_pyparsing = Parser(grammar_fn=Parser.PYPARSING_PARSER)
print(f"Parser(grammar_fn=Parser.PYPARSING_PARSER) -> Type: {type(p_pyparsing).__name__}")
print(p_pyparsing.which_grammar())