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bpo-29974: Change typing.TYPE_CHECKING doc example #982

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Apr 26, 2017
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bpo-29974: Change typing.TYPE_CHECKING doc example #982

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9 changes: 7 additions & 2 deletions Doc/library/typing.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1005,5 +1005,10 @@ The module defines the following classes, functions and decorators:
if TYPE_CHECKING:
import expensive_mod

def fun():
local_var: expensive_mod.some_type = other_fun()
def fun(arg: 'expensive_mod.SomeType') -> None:
local_var: expensive_mod.AnotherType = other_fun()

Note that the first type annotation must be enclosed in quotes, making it a
"forward reference", to hide the ``expensive_mod`` reference from the
interpreter runtime. Type annotations for local variables are not
evaluated, so the second annotation does not need to be enclosed in quotes.