unroll.py 文件源码

def _visit_For(self, node):
        if not isinstance(node.target, ast.Name):
            return

        # for i in (1, 2, 3): ...
        if not isinstance(node.iter, ast.Constant):
            return
        iter_value = node.iter.value
        if not isinstance(iter_value, tuple):
            return
        if not(1 <= len(iter_value) <= self.config.unroll_loops):
            return

        # don't optimize if 'break' or 'continue' is found in the loop body
        found = None
        def find_callback(node):
            nonlocal found
            found = node
            return False

        # FIXME: restrict this the current scope
        # (don't enter class/function def/list comprehension/...)
        visitor = FindNodes(CANNOT_UNROLL, find_callback)
        visitor.visit(node)
        if found is not None:
            self.log(node,
                     "cannot unroll loop: %s is used at line %s",
                     compact_dump(found),
                     found.lineno)
            return

        name = node.target.id
        body = node.body

        # replace 'for i in (1, 2, 3): body' with...
        new_node = []
        for value in node.iter.value:
            value_ast = self.new_constant(node.iter, value)
            if value_ast is None:
                return

            # 'i = 1'
            name_ast = ast.Name(id=name, ctx=ast.Store())
            copy_lineno(node, name_ast)
            assign = ast.Assign(targets=[name_ast],
                                value=value_ast)
            copy_lineno(node, assign)
            new_node.append(assign)

            # duplicate 'body'
            new_node.extend(body)

        if node.orelse:
            new_node.extend(node.orelse)

        self.log(node, "unroll loop (%s iterations)", len(node.iter.value))

        return new_node