Method simplify_once

dask/_expr.py:367–435

Simplify an expression This leverages the ``._simplify_down`` and ``._simplify_up`` methods defined on each class Parameters ---------- dependents: defaultdict[list] The dependents for every node. simplified: dict Cache of si

(self, dependents: defaultdict, simplified: dict)

        return expr

    def simplify_once(self, dependents: defaultdict, simplified: dict):
        """Simplify an expression

        This leverages the ``._simplify_down`` and ``._simplify_up``
        methods defined on each class

        Parameters
        ----------

        dependents: defaultdict[list]
            The dependents for every node.
        simplified: dict
            Cache of simplified expressions for these dependents.

        Returns
        -------
        expr:
            output expression
        """
        # Check if we've already simplified for these dependents
        if self._name in simplified:
            return simplified[self._name]

        expr = self

        while True:
            out = expr._simplify_down()
            if out is None:
                out = expr
            if not isinstance(out, Expr):
                return out
            if out._name != expr._name:
                expr = out

            # Allow children to simplify their parents
            for child in expr.dependencies():
                out = child._simplify_up(expr, dependents)
                if out is None:
                    out = expr

                if not isinstance(out, Expr):
                    return out
                if out is not expr and out._name != expr._name:
                    expr = out
                    break

            # Rewrite all of the children
            new_operands = []
            changed = False
            for operand in expr.operands:
                if isinstance(operand, Expr):
                    # Bandaid for now, waiting for Singleton
                    dependents[operand._name].append(weakref.ref(expr))
                    new = operand.simplify_once(
                        dependents=dependents, simplified=simplified
                    )
                    simplified[operand._name] = new
                    if new._name != operand._name: