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annotations: expand documentation on "simple" assignment targets (#120535)
This behavior is rather surprising and it was not clearly specified. Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
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2 changed files with 12 additions and 5 deletions
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@ -891,9 +891,13 @@ Statements
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An assignment with a type annotation. ``target`` is a single node and can
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be a :class:`Name`, a :class:`Attribute` or a :class:`Subscript`.
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``annotation`` is the annotation, such as a :class:`Constant` or :class:`Name`
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node. ``value`` is a single optional node. ``simple`` is a boolean integer
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set to True for a :class:`Name` node in ``target`` that do not appear in
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between parenthesis and are hence pure names and not expressions.
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node. ``value`` is a single optional node.
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``simple`` is always either 0 (indicating a "complex" target) or 1
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(indicating a "simple" target). A "simple" target consists solely of a
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:class:`Name` node that does not appear between parentheses; all other
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targets are considered complex. Only simple targets appear in
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the :attr:`__annotations__` dictionary of modules and classes.
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.. doctest::
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@ -333,7 +333,9 @@ statement, of a variable or attribute annotation and an optional assignment stat
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The difference from normal :ref:`assignment` is that only a single target is allowed.
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For simple names as assignment targets, if in class or module scope,
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The assignment target is considered "simple" if it consists of a single
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name that is not enclosed in parentheses.
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For simple assignment targets, if in class or module scope,
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the annotations are evaluated and stored in a special class or module
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attribute :attr:`__annotations__`
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that is a dictionary mapping from variable names (mangled if private) to
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@ -341,7 +343,8 @@ evaluated annotations. This attribute is writable and is automatically
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created at the start of class or module body execution, if annotations
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are found statically.
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For expressions as assignment targets, the annotations are evaluated if
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If the assignment target is not simple (an attribute, subscript node, or
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parenthesized name), the annotation is evaluated if
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in class or module scope, but not stored.
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If a name is annotated in a function scope, then this name is local for
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