+
−# -*- coding: utf-8 -*-
+
−"""The optimizer tries to constant fold expressions and modify the AST
+
−in place so that it should be faster to evaluate.
+
−
+
−Because the AST does not contain all the scoping information and the
+
−compiler has to find that out, we cannot do all the optimizations we
+
−want. For example, loop unrolling doesn't work because unrolled loops
+
−would have a different scope. The solution would be a second syntax tree
+
−that stored the scoping rules.
+
−"""
+
−from . import nodes
+
−from .visitor import NodeTransformer
+
−
+
−
+
−def optimize(node, environment):
+
−    """The context hint can be used to perform an static optimization
+
−    based on the context given."""
+
−    optimizer = Optimizer(environment)
+
−    return optimizer.visit(node)
+
−
+
−
+
−class Optimizer(NodeTransformer):
+
−    def __init__(self, environment):
+
−        self.environment = environment
+
−
+
−    def generic_visit(self, node, *args, **kwargs):
+
−        node = super(Optimizer, self).generic_visit(node, *args, **kwargs)
+
−
+
−        # Do constant folding. Some other nodes besides Expr have
+
−        # as_const, but folding them causes errors later on.
+
−        if isinstance(node, nodes.Expr):
+
−            try:
+
−                return nodes.Const.from_untrusted(
+
−                    node.as_const(args[0] if args else None),
+
−                    lineno=node.lineno,
+
−                    environment=self.environment,
+
−                )
+
−            except nodes.Impossible:
+
−                pass
+
−
+
−        return node