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stbi/Lib/site-packages/pip/_internal/utils/typing.py

+"""For neatly implementing static typing in pip.
+
+`mypy` - the static type analysis tool we use - uses the `typing` module, which
+provides core functionality fundamental to mypy's functioning.
+
+Generally, `typing` would be imported at runtime and used in that fashion -
+it acts as a no-op at runtime and does not have any run-time overhead by
+design.
+
+As it turns out, `typing` is not vendorable - it uses separate sources for
+Python 2/Python 3. Thus, this codebase can not expect it to be present.
+To work around this, mypy allows the typing import to be behind a False-y
+optional to prevent it from running at runtime and type-comments can be used
+to remove the need for the types to be accessible directly during runtime.
+
+This module provides the False-y guard in a nicely named fashion so that a
+curious maintainer can reach here to read this.
+
+In pip, all static-typing related imports should be guarded as follows:
+
+    from pip._internal.utils.typing import MYPY_CHECK_RUNNING
+
+    if MYPY_CHECK_RUNNING:
+        from typing import ...
+
+Ref: https://github.com/python/mypy/issues/3216
+"""
+
+MYPY_CHECK_RUNNING = False
+
+
+if MYPY_CHECK_RUNNING:
+    from typing import cast
+else:
+    # typing's cast() is needed at runtime, but we don't want to import typing.
+    # Thus, we use a dummy no-op version, which we tell mypy to ignore.
+    def cast(type_, value):  # type: ignore
+        return value