Method validate_and_transform_accessors

mypy/checkstrformat.py:616–672

Validate and transform (in-place) format field accessors. On error, report it and return False. The transformations include replacing the dummy variable with actual replacement expression and translating any name expressions in an index into strings, so that this will work:

(
        self,
        temp_ast: Expression,
        original_repl: Expression,
        spec: ConversionSpecifier,
        ctx: Context,
    )

        return temp_ast

    def validate_and_transform_accessors(
        self,
        temp_ast: Expression,
        original_repl: Expression,
        spec: ConversionSpecifier,
        ctx: Context,
    ) -> bool:
        """Validate and transform (in-place) format field accessors.

        On error, report it and return False. The transformations include replacing the dummy
        variable with actual replacement expression and translating any name expressions in an
        index into strings, so that this will work:

            class User(TypedDict):
                name: str
                id: int
            u: User
            '{[id]:d} -> {[name]}'.format(u)
        """
        if not isinstance(temp_ast, (MemberExpr, IndexExpr)):
            self.msg.fail(
                "Only index and member expressions are allowed in"
                ' format field accessors; got "{}"'.format(spec.field),
                ctx,
                code=codes.STRING_FORMATTING,
            )
            return False
        if isinstance(temp_ast, MemberExpr):
            node = temp_ast.expr
        else:
            node = temp_ast.base
            if not isinstance(temp_ast.index, (NameExpr, IntExpr)):
                assert spec.key, "Call this method only after auto-generating keys!"
                assert spec.field
                self.msg.fail(
                    'Invalid index expression in format field accessor "{}"'.format(
                        spec.field[len(spec.key) :]
                    ),
                    ctx,
                    code=codes.STRING_FORMATTING,
                )
                return False
            if isinstance(temp_ast.index, NameExpr):
                temp_ast.index = StrExpr(temp_ast.index.name)
        if isinstance(node, NameExpr) and node.name == DUMMY_FIELD_NAME:
            # Replace it with the actual replacement expression.
            assert isinstance(temp_ast, (IndexExpr, MemberExpr))  # XXX: this is redundant
            if isinstance(temp_ast, IndexExpr):
                temp_ast.base = original_repl
            else:
                temp_ast.expr = original_repl
            return True
        node.line = ctx.line
        node.column = ctx.column
        return self.validate_and_transform_accessors(
            node, original_repl=original_repl, spec=spec, ctx=ctx
        )