Class PlaceholderNode

mypy/nodes.py:4709–4780

Temporary symbol node that will later become a real SymbolNode. These are only present during semantic analysis when using the new semantic analyzer. These are created if some essential dependencies of a definition are not yet complete. A typical use is for names imported from a mo

class PlaceholderNode(SymbolNode):
    """Temporary symbol node that will later become a real SymbolNode.

    These are only present during semantic analysis when using the new
    semantic analyzer. These are created if some essential dependencies
    of a definition are not yet complete.

    A typical use is for names imported from a module which is still
    incomplete (within an import cycle):

      from m import f  # Initially may create PlaceholderNode

    This is particularly important if the imported shadows a name from
    an enclosing scope or builtins:

      from m import int  # Placeholder avoids mixups with builtins.int

    Another case where this is useful is when there is another definition
    or assignment:

      from m import f
      def f() -> None: ...

    In the above example, the presence of PlaceholderNode allows us to
    handle the second definition as a redefinition.

    They are also used to create PlaceholderType instances for types
    that refer to incomplete types. Example:

      class C(Sequence[C]): ...

    We create a PlaceholderNode (with becomes_typeinfo=True) for C so
    that the type C in Sequence[C] can be bound.

    Attributes:

      fullname: Full name of the PlaceholderNode.
      node: AST node that contains the definition that caused this to
          be created. This is useful for tracking order of incomplete definitions
          and for debugging.
      becomes_typeinfo: If True, this refers something that could later
          become a TypeInfo. It can't be used with type variables, in
          particular, as this would cause issues with class type variable
          detection.

    The long-term purpose of placeholder nodes/types is to evolve into
    something that can support general recursive types.
    """

    __slots__ = ("_fullname", "node", "becomes_typeinfo")

    def __init__(
        self, fullname: str, node: Node, line: int, *, becomes_typeinfo: bool = False
    ) -> None:
        self._fullname = fullname
        self.node = node
        self.becomes_typeinfo = becomes_typeinfo
        self.line = line