I want to parse strings like alpha OR beta gamma where a missing operator (in this case between beta and gamma a implicit AND is used.

Here is the code I tried:

import pyparsing as pp


class Term:
    def __init__(self, tokens: pp.ParseResults):
        self.value = str(tokens[0])

    def __repr__(self) -> str:
        return f"Term({self.value})"


class BinaryOp:
    def __init__(self, tokens: pp.ParseResults) -> None:
        self.op = tokens[0][1]
        self.left = tokens[0][0]
        self.right = tokens[0][2]

    def __repr__(self) -> str:
        return f"BinaryOp({self.op}, {self.left}, {self.right})"


and_ = pp.Keyword("AND")
or_ = pp.Keyword("OR")
word = (~(and_ | or_) + pp.Word(pp.alphanums + pp.alphas8bit + "_")).set_parse_action(Term)

expression = pp.infix_notation(
    word,
    [
        (pp.Optional(and_), 2, pp.opAssoc.LEFT, BinaryOp),
        (or_, 2, pp.opAssoc.LEFT, BinaryOp),
    ],
)

input_string = "alpha OR beta gamma"
parsed_result = expression.parseString(input_string)
print(parsed_result.asList())

The output is [BinaryOp(OR, Term(alpha), Term(beta))], so the implicit AND and gamma is not parsed. How could I fix this?