Class ColumnDefault

lib/sqlalchemy/sql/schema.py:3410–3492

A plain default value on a column. This could correspond to a constant, a callable function, or a SQL clause. :class:`.ColumnDefault` is generated automatically whenever the ``default``, ``onupdate`` arguments of :class:`_schema.Column` are used. A :class:`.ColumnDefault`

class ColumnDefault(DefaultGenerator, ABC):
    """A plain default value on a column.

    This could correspond to a constant, a callable function,
    or a SQL clause.

    :class:`.ColumnDefault` is generated automatically
    whenever the ``default``, ``onupdate`` arguments of
    :class:`_schema.Column` are used.  A :class:`.ColumnDefault`
    can be passed positionally as well.

    For example, the following::

        Column("foo", Integer, default=50)

    Is equivalent to::

        Column("foo", Integer, ColumnDefault(50))

    """

    arg: Any

    @overload
    def __new__(
        cls, arg: Callable[..., Any], for_update: bool = ...
    ) -> CallableColumnDefault: ...

    @overload
    def __new__(
        cls, arg: ColumnElement[Any], for_update: bool = ...
    ) -> ColumnElementColumnDefault: ...

    # if I return ScalarElementColumnDefault here, which is what's actually
    # returned, mypy complains that
    # overloads overlap w/ incompatible return types.
    @overload
    def __new__(cls, arg: object, for_update: bool = ...) -> ColumnDefault: ...

    def __new__(
        cls, arg: Any = None, for_update: bool = False
    ) -> ColumnDefault:
        """Construct a new :class:`.ColumnDefault`.


        :param arg: argument representing the default value.
         May be one of the following:

         * a plain non-callable Python value, such as a
           string, integer, boolean, or other simple type.
           The default value will be used as is each time.
         * a SQL expression, that is one which derives from
           :class:`_expression.ColumnElement`.  The SQL expression will
           be rendered into the INSERT or UPDATE statement,
           or in the case of a primary key column when
           RETURNING is not used may be
           pre-executed before an INSERT within a SELECT.
         * A Python callable.  The function will be invoked for each