Function group_comparison_operands

mypy/checker.py:9410–9507

Group a series of comparison operands together chained by any operand in the 'operators_to_group' set. All other pairwise operands are kept in groups of size 2. For example, suppose we have the input comparison expression: x0 == x1 == x2 < x3 < x4 is x5 is x6 is not x7 is not x

(
    pairwise_comparisons: Iterable[tuple[str, Expression, Expression]],
    operand_to_literal_hash: Mapping[int, Key],
    operators_to_group: set[str],
)

def group_comparison_operands(
    pairwise_comparisons: Iterable[tuple[str, Expression, Expression]],
    operand_to_literal_hash: Mapping[int, Key],
    operators_to_group: set[str],
) -> list[tuple[str, list[int]]]:
    """Group a series of comparison operands together chained by any operand
    in the 'operators_to_group' set. All other pairwise operands are kept in
    groups of size 2.

    For example, suppose we have the input comparison expression:

        x0 == x1 == x2 < x3 < x4 is x5 is x6 is not x7 is not x8

    If we get these expressions in a pairwise way (e.g. by calling ComparisonExpr&#x27;s
    'pairwise()' method), we get the following as input:

        [('==', x0, x1), ('==', x1, x2), ('<', x2, x3), ('<', x3, x4),
         ('is', x4, x5), ('is', x5, x6), ('is not', x6, x7), ('is not', x7, x8)]

    If `operators_to_group` is the set {'==', 'is'}, this function will produce
    the following "simplified operator list":

       [("==", [0, 1, 2]), ("<", [2, 3]), ("<", [3, 4]),
        ("is", [4, 5, 6]), ("is not", [6, 7]), ("is not", [7, 8])]

    Note that (a) we yield *indices* to the operands rather then the operand
    expressions themselves and that (b) operands used in a consecutive chain
    of '==' or 'is' are grouped together.

    If two of these chains happen to contain operands with the same underlying
    literal hash (e.g. are assignable and correspond to the same expression),
    we combine those chains together. For example, if we had:

        same == x < y == same

    ...and if 'operand_to_literal_hash' contained the same values for the indices
    0 and 3, we&#x27;d produce the following output:

        [("==", [0, 1, 2, 3]), ("<", [1, 2])]

    But if the 'operand_to_literal_hash' did *not* contain an entry, we&#x27;d instead
    default to returning:

        [("==", [0, 1]), ("<", [1, 2]), ("==", [2, 3])]

    This function is currently only used to assist with type-narrowing refinements
    and is extracted out to a helper function so we can unit test it.
    """
    groups: dict[str, DisjointDict[Key, int]] = {op: DisjointDict() for op in operators_to_group}

    simplified_operator_list: list[tuple[str, list[int]]] = []
    last_operator: str | None = None
    current_indices: set[int] = set()
    current_hashes: set[Key] = set()
    for i, (operator, left_expr, right_expr) in enumerate(pairwise_comparisons):
        if last_operator is None:
            last_operator = operator