An entry of None in sys.path_importer_cache represents a negative/missing finder for a path, so clearing it out makes sense.

Original patch by Alexander Belopolsky.  Patch by Skip Montanaro.

* Add a test for frozen with unhashable field value.
* Improve a comment.

This removes a hack and replaces it with a proper
mapping {'list': 'List', 'dict': 'Dict', ...}.

Different paths are executed for normal exit and for leaving
the 'async with' block with 'break', 'continue' or 'return'.

This makes performance better and produces shorter pickles. This change is backwards compatible up to the oldest currently supported version of Python (3.4).

Py_UNICODE is deprecated since Python 3.3.
But the deprecation is missed in the c-api/arg document.

when __aenter__() or __aexit__() return non-awaitable object.

Followup to primary PR for the issue, GH-6344.

A 'u' string prefix cannot be paired with either 'r' or 'f'.  Consistently
color as much of the prefix, starting at the right, as is valid.

Build and link with private copy of Tcl/Tk 8.6 for the macOS 10.6+
installer. The 10.9+ installer variant already does this.  This means that
the Python 3.7 provided by the python.org macOS installers no longer need or
use any external versions of Tcl/Tk, either system-provided or user-
installed, such as ActiveTcl.

Most of them have been added in 3.7.

Forcing the macOS IDLE.app gui process to launch in 32-mode was
a necessary hack for old versions of Tk (Aqua Carbon as in Tk 8.4
and early versions of 8.5); it is not needed for current versions
of Tk.  Since 32-bit launching will no longer be supported on
future releases of macOS, allow IDLE.app to launch in 64-bit mode.

* Also in docs