Module opshin.rewrite.rewrite_annotate_fallthrough

Classes

class RewriteAnnotateFallthrough

A :class:NodeVisitor subclass that walks the abstract syntax tree and allows modification of nodes.

The NodeTransformer will walk the AST and use the return value of the visitor methods to replace or remove the old node. If the return value of the visitor method is None, the node will be removed from its location, otherwise it is replaced with the return value. The return value may be the original node in which case no replacement takes place.

Here is an example transformer that rewrites all occurrences of name lookups (foo) to data['foo']::

class RewriteName(NodeTransformer):

   def visit_Name(self, node):
       return Subscript(
           value=Name(id='data', ctx=Load()),
           slice=Constant(value=node.id),
           ctx=node.ctx
       )

Keep in mind that if the node you're operating on has child nodes you must either transform the child nodes yourself or call the :meth:generic_visit method for the node first.

For nodes that were part of a collection of statements (that applies to all statement nodes), the visitor may also return a list of nodes rather than just a single node.

Usually you use the transformer like this::

node = YourTransformer().visit(node)

Expand source code

class RewriteAnnotateFallthrough(CompilingNodeTransformer):
    step = "Annotating statement fallthrough"
    compound_statement_types = (Module, FunctionDef, ClassDef, If, For, While)

    @staticmethod
    def expr_is_definitely_false(node):
        if isinstance(node, Constant):
            return not bool(node.value)
        if (
            isinstance(node, Call)
            and isinstance(node.func, Name)
            and (node.func.id == SPECIAL_BOOL or node.func.orig_id == SPECIAL_BOOL)
            and len(node.args) == 1
            and not node.keywords
        ):
            return RewriteAnnotateFallthrough.expr_is_definitely_false(node.args[0])
        return False

    def generic_visit(self, node):
        if isinstance(node, self.compound_statement_types):
            node = copy(node)
        visited = super().generic_visit(node)
        if isinstance(visited, ast.stmt):
            visited.can_fall_through = getattr(visited, "can_fall_through", True)
        if isinstance(visited, self.compound_statement_types):
            return annotate_compound_statement_fallthrough(visited)
        return visited

    def visit_Return(self, node: Return) -> Return:
        return_cp = self.generic_visit(copy(node))
        return_cp.can_fall_through = False
        return return_cp

    def visit_Assert(self, node: Assert) -> Assert:
        assert_cp = self.generic_visit(copy(node))
        assert_cp.can_fall_through = not self.expr_is_definitely_false(assert_cp.test)
        return assert_cp

Ancestors

• CompilingNodeTransformer
• TypedNodeTransformer
• ast.NodeTransformer
• ast.NodeVisitor

Class variables

var compound_statement_types

The type of the None singleton.

var step

Inherited from: CompilingNodeTransformer.step

The type of the None singleton.

Static methods

def expr_is_definitely_false(node)

Expand source code

@staticmethod
def expr_is_definitely_false(node):
    if isinstance(node, Constant):
        return not bool(node.value)
    if (
        isinstance(node, Call)
        and isinstance(node.func, Name)
        and (node.func.id == SPECIAL_BOOL or node.func.orig_id == SPECIAL_BOOL)
        and len(node.args) == 1
        and not node.keywords
    ):
        return RewriteAnnotateFallthrough.expr_is_definitely_false(node.args[0])
    return False

Methods

def generic_visit(self, node)

Called if no explicit visitor function exists for a node.

Expand source code

def generic_visit(self, node):
    if isinstance(node, self.compound_statement_types):
        node = copy(node)
    visited = super().generic_visit(node)
    if isinstance(visited, ast.stmt):
        visited.can_fall_through = getattr(visited, "can_fall_through", True)
    if isinstance(visited, self.compound_statement_types):
        return annotate_compound_statement_fallthrough(visited)
    return visited

def visit(self, node)

Inherited from: CompilingNodeTransformer.visit

Visit a node.

def visit_Assert(self, node: ast.Assert) ‑> ast.Assert

Expand source code

def visit_Assert(self, node: Assert) -> Assert:
    assert_cp = self.generic_visit(copy(node))
    assert_cp.can_fall_through = not self.expr_is_definitely_false(assert_cp.test)
    return assert_cp

def visit_Return(self, node: ast.Return) ‑> ast.Return

Expand source code

def visit_Return(self, node: Return) -> Return:
    return_cp = self.generic_visit(copy(node))
    return_cp.can_fall_through = False
    return return_cp