Function _determine_attrib_eq_order

src/attr/_make.py:1256–1296

Validate the combination of *cmp*, *eq*, and *order*. Derive the effective values of eq and order. If *eq* is None, set it to *default_eq*.

(cmp, eq, order, default_eq)

def _determine_attrib_eq_order(cmp, eq, order, default_eq):
    """
    Validate the combination of *cmp*, *eq*, and *order*. Derive the effective
    values of eq and order.  If *eq* is None, set it to *default_eq*.
    """
    if cmp is not None and any((eq is not None, order is not None)):
        msg = "Don't mix `cmp` with `eq' and `order`."
        raise ValueError(msg)

    def decide_callable_or_boolean(value):
        """
        Decide whether a key function is used.
        """
        if callable(value):
            value, key = True, value
        else:
            key = None
        return value, key

    # cmp takes precedence due to bw-compatibility.
    if cmp is not None:
        cmp, cmp_key = decide_callable_or_boolean(cmp)
        return cmp, cmp_key, cmp, cmp_key

    # If left None, equality is set to the specified default and ordering
    # mirrors equality.
    if eq is None:
        eq, eq_key = default_eq, None
    else:
        eq, eq_key = decide_callable_or_boolean(eq)

    if order is None:
        order, order_key = eq, eq_key
    else:
        order, order_key = decide_callable_or_boolean(order)

    if eq is False and order is True:
        msg = "`order` can only be True if `eq` is True too."
        raise ValueError(msg)

    return eq, eq_key, order, order_key


def _determine_whether_to_implement(