How to use the libcst._nodes.expression.BaseExpression function in libcst

def _codegen_impl(self, state: CodegenState) -> None:
        with self._parenthesize(state):
            self.func._codegen(state)
            self.whitespace_after_func._codegen(state)
            state.add_token("(")
            self.whitespace_before_args._codegen(state)
            lastarg = len(self.args) - 1
            for i, arg in enumerate(self.args):
                arg._codegen(state, default_comma=(i != lastarg))
            state.add_token(")")


@add_slots
@dataclass(frozen=True)
class Await(BaseExpression):
    """
    An await expression. Await expressions are only valid inside the body of an
    asynchronous :class:`FunctionDef` or (as of Python 3.7) inside of an asynchronous
    :class:`GeneratorExp` nodes.
    """

    #: The actual expression we need to wait for.
    expression: BaseExpression

    lpar: Sequence[LeftParen] = ()
    #: Sequence of parenthesis for precedence dictation.
    rpar: Sequence[RightParen] = ()

    #: Whitespace that appears after the ``async`` keyword, but before the inner
    #: ``expression``.
    whitespace_after_await: BaseParenthesizableWhitespace = SimpleWhitespace.field(" ")

Python's grammar defines all expression as valid in this position, but the AST
    compiler further restricts the allowed types, which is what this type attempts to
    express.

    This is similar to a :class:`BaseDelTargetExpression`, but it also includes
    :class:`StarredElement` as a valid node.

    The set of valid nodes are defined as part of `CPython's AST context computation
    `_.
    """

    pass


class BaseDelTargetExpression(BaseExpression, ABC):
    """
    An expression that's valid on the right side of a :class:`Del` statement.

    Python's grammar defines all expression as valid in this position, but the AST
    compiler further restricts the allowed types, which is what this type attempts to
    express.

    This is similar to a :class:`BaseAssignTargetExpression`, but it excludes
    :class:`StarredElement`.

    The set of valid nodes are defined as part of `CPython's AST context computation
    `_ and as part
    of `CPython's bytecode compiler
    `_.
    """

semicolon._codegen(state)


@add_slots
@dataclass(frozen=True)
class AnnAssign(BaseSmallStatement):
    """
    An assignment statement such as ``x: int = 5`` or ``x: int``. This only
    allows for one assignment target unlike :class:`Assign` but it includes
    a variable annotation. Also unlike :class:`Assign`, the assignment target
    is optional, as it is possible to annotate an expression without assigning
    to it.
    """

    #: The target that is being annotated and possibly assigned to.
    target: BaseExpression

    #: The annotation for the target.
    annotation: Annotation

    #: The optional expression being assigned to the target.
    value: Optional[BaseExpression] = None

    #: The equals sign used to denote assignment if there is a value.
    equal: Union[AssignEqual, MaybeSentinel] = MaybeSentinel.DEFAULT

    #: Optional semicolon when this is used in a statement line. This semicolon
    #: owns the whitespace on both sides of it when it is used.
    semicolon: Union[Semicolon, MaybeSentinel] = MaybeSentinel.DEFAULT

    def _validate(self) -> None:
        if self.value is None and isinstance(self.equal, AssignEqual):

)

    def _visit_and_replace_children(self, visitor: CSTVisitorT) -> "ComparisonTarget":
        return ComparisonTarget(
            operator=visit_required(self, "operator", self.operator, visitor),
            comparator=visit_required(self, "comparator", self.comparator, visitor),
        )

    def _codegen_impl(self, state: CodegenState) -> None:
        self.operator._codegen(state)
        self.comparator._codegen(state)


@add_slots
@dataclass(frozen=True)
class Comparison(BaseExpression):
    """
    A comparison between multiple values such as ``x < y``, ``x < y < z``, or
    ``x in [y, z]``. These comparisions typically result in boolean values.

    Unlike :class:`BinaryOperation` and :class:`BooleanOperation`, comparisons are not
    restricted to a left and right child. Instead they can contain an arbitrary number
    of :class:`ComparisonTarget` children.

    ``x < y < z`` is not equivalent to ``(x < y) < z`` or ``x < (y < z)``. Instead,
    it's roughly equivalent to ``x < y and y < z``.

    For more details, see `Python's documentation on comparisons
    `_.

    ::

lpar=visit_sequence(self, "lpar", self.lpar, visitor),
            value=self.value,
            rpar=visit_sequence(self, "rpar", self.rpar, visitor),
        )

    def _validate(self) -> None:
        super(Imaginary, self)._validate()
        if not re.fullmatch(IMAGNUMBER_RE, self.value):
            raise CSTValidationError("Number is not a valid imaginary.")

    def _codegen_impl(self, state: CodegenState) -> None:
        with self._parenthesize(state):
            state.add_token(self.value)


class BaseString(BaseExpression, ABC):
    """
    A type that can be used anywhere that you need to take any string. This includes
    :class:`SimpleString`, :class:`ConcatenatedString`, and :class:`FormattedString`.
    """

    pass


class _BasePrefixedString(BaseString, ABC):
    @abstractmethod
    def _get_prefix(self) -> str:
        ...

    def _safe_to_use_with_word_operator(self, position: ExpressionPosition) -> bool:
        """
        ``"a"in"abc`` is okay, but if you add a prefix, (e.g. ``b"a"inb"abc"``), the string

TYPED_FUNCTION_RETURN_MAPPING: TypingDict[Type[CSTNode], object] = {
    Add: BaseBinaryOp,
    AddAssign: BaseAugOp,
    And: BaseBooleanOp,
    AnnAssign: Union[BaseSmallStatement, RemovalSentinel],
    Annotation: Annotation,
    Arg: Union[Arg, RemovalSentinel],
    AsName: AsName,
    Assert: Union[BaseSmallStatement, RemovalSentinel],
    Assign: Union[BaseSmallStatement, RemovalSentinel],
    AssignEqual: Union[AssignEqual, MaybeSentinel],
    AssignTarget: Union[AssignTarget, RemovalSentinel],
    Asynchronous: Asynchronous,
    Attribute: BaseExpression,
    AugAssign: Union[BaseSmallStatement, RemovalSentinel],
    Await: BaseExpression,
    BinaryOperation: BaseExpression,
    BitAnd: BaseBinaryOp,
    BitAndAssign: BaseAugOp,
    BitInvert: BaseUnaryOp,
    BitOr: BaseBinaryOp,
    BitOrAssign: BaseAugOp,
    BitXor: BaseBinaryOp,
    BitXorAssign: BaseAugOp,
    BooleanOperation: BaseExpression,
    Break: Union[BaseSmallStatement, RemovalSentinel],
    Call: BaseExpression,
    ClassDef: Union[BaseStatement, RemovalSentinel],
    Colon: Union[Colon, MaybeSentinel],
    Comma: Union[Comma, MaybeSentinel],

self.name._codegen(state)


@add_slots
@dataclass(frozen=True)
class ExceptHandler(CSTNode):
    """
    An ``except`` clause that appears optionally after a :class:`Try` statement.
    """

    #: The body of the except.
    body: BaseSuite

    #: The type of exception this catches. Can be a tuple in some cases,
    #: or ``None`` if the code is catching all exceptions.
    type: Optional[BaseExpression] = None

    #: The optional name that a caught exception is assigned to.
    name: Optional[AsName] = None

    #: Sequence of empty lines appearing before this compound statement line.
    leading_lines: Sequence[EmptyLine] = ()

    #: The whitespace between the ``except`` keyword and the type attribute.
    whitespace_after_except: SimpleWhitespace = SimpleWhitespace.field(" ")

    #: The whitespace after any type or name node (whichever comes last) and
    #: the colon.
    whitespace_before_colon: SimpleWhitespace = SimpleWhitespace.field("")

    def _validate(self) -> None:
        name = self.name

equal = self.equal
            if equal is MaybeSentinel.DEFAULT and self.keyword is not None:
                state.add_token(" = ")
            elif isinstance(equal, AssignEqual):
                equal._codegen(state)
            self.value._codegen(state)

        comma = self.comma
        if comma is MaybeSentinel.DEFAULT and default_comma:
            state.add_token(", ")
        elif isinstance(comma, Comma):
            comma._codegen(state)
        self.whitespace_after_arg._codegen(state)


class _BaseExpressionWithArgs(BaseExpression, ABC):
    """
    Arguments are complicated enough that we can't represent them easily
    in typing. So, we have common validation functions here.
    """

    #: Sequence of arguments that will be passed to the function call.
    args: Sequence[Arg] = ()

    def _check_kwargs_or_keywords(
        self, arg: Arg
    ) -> Optional[Callable[[Arg], Callable]]:
        """
        Validates that we only have a mix of "keyword=arg" and "**arg" expansion.
        """

        if arg.keyword is not None:

def _codegen_impl(self, state: CodegenState, default_space: str = "") -> None:
        whitespace_before_from = self.whitespace_before_from
        if isinstance(whitespace_before_from, BaseParenthesizableWhitespace):
            whitespace_before_from._codegen(state)
        else:
            state.add_token(default_space)

        with state.record_syntactic_position(self):
            state.add_token("from")
            self.whitespace_after_from._codegen(state)
            self.item._codegen(state)


@add_slots
@dataclass(frozen=True)
class Yield(BaseExpression):
    """
    A yield expression similar to ``yield x`` or ``yield from fun()``.

    To learn more about the ways that yield can be used in generators, refer to
    `Python's language reference
    `__.
    """

    #: The value yielded from the generator, in the case of a :class:`From` clause, a
    #: sub-generator to iterate over.
    value: Optional[Union[BaseExpression, From]] = None

    lpar: Sequence[LeftParen] = ()
    #: Sequence of parenthesis for precedence dictation.
    rpar: Sequence[RightParen] = ()

lpar=visit_sequence(self, "lpar", self.lpar, visitor),
            left=visit_required(self, "left", self.left, visitor),
            comparisons=visit_sequence(self, "comparisons", self.comparisons, visitor),
            rpar=visit_sequence(self, "rpar", self.rpar, visitor),
        )

    def _codegen_impl(self, state: CodegenState) -> None:
        with self._parenthesize(state):
            self.left._codegen(state)
            for comp in self.comparisons:
                comp._codegen(state)


@add_slots
@dataclass(frozen=True)
class UnaryOperation(BaseExpression):
    """
    Any generic unary expression, such as ``not x`` or ``-x``. :class:`UnaryOperation`
    nodes apply a :class:`BaseUnaryOp` to an expression.
    """

    #: The unary operator that applies some operation (e.g. negation) to the
    #: ``expression``.
    operator: BaseUnaryOp

    #: The expression that should be transformed (e.g. negated) by the operator to
    #: create a new value.
    expression: BaseExpression

    lpar: Sequence[LeftParen] = ()
    #: Sequence of parenthesis for precedence dictation.
    rpar: Sequence[RightParen] = ()