Since `SourceFileLoader.set_data()` catches exceptions raised by `_write_atomic()` and logs an informative message consequently, always logging successful outcome in 'SourceLoader.get_code()' seems redundant.  



https://bugs.python.org/issue35024

In some development setups it is inconvenient or impossible to write bytecode
caches to the code tree, but the bytecode caches are still useful. The
PYTHONPYCACHEPREFIX environment variable allows specifying an alternate
location for cached bytecode files, within which a directory tree mirroring the code
tree will be created. This cache tree is then used (for both reading and writing)
instead of the local `__pycache__` subdirectory within each source directory.

Exposed at runtime as sys.pycache_prefix (defaulting to None), and can
be set from the CLI as "-X pycache_prefix=path".

Patch by Carl Meyer.

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

* Added new opcode END_ASYNC_FOR.
* Setting global StopAsyncIteration no longer breaks "async for" loops.
* Jumping into an "async for" loop is now disabled.
* Jumping out of an "async for" loop no longer corrupts the stack.
* Simplify the compiler.

Co-authored-by: Mark Shannon <mark@hotpy.org>
Co-authored-by: Antoine Pitrou <antoine@python.org>

* Make sure ``__spec__.loader`` matches ``__loader__`` for namespace packages.
* Make sure ``__spec__.origin` matches ``__file__`` for namespace packages.

https://bugs.python.org/issue32303
https://bugs.python.org/issue32305

Python now supports checking bytecode cache up-to-dateness with a hash of the
source contents rather than volatile source metadata. See the PEP for details.

While a fairly straightforward idea, quite a lot of code had to be modified due
to the pervasiveness of pyc implementation details in the codebase. Changes in
this commit include:

- The core changes to importlib to understand how to read, validate, and
  regenerate hash-based pycs.

- Support for generating hash-based pycs in py_compile and compileall.

- Modifications to our siphash implementation to support passing a custom
  key. We then expose it to importlib through _imp.

- Updates to all places in the interpreter, standard library, and tests that
  manually generate or parse pyc files to grok the new format.

- Support in the interpreter command line code for long options like
  --check-hash-based-pycs.

- Tests and documentation for all of the above.

* Trivial cleanups following bpo-31370

* Also cleanup the "importlib._bootstrap_external" module

Special thanks to INADA Naoki for pushing the patch through
the last mile, Serhiy Storchaka for reviewing the code, and to
Victor Stinner for suggesting the idea (originally implemented
in the PyPy project).

Handling zero-argument super() in __init_subclass__ and
__set_name__ involved moving __class__ initialisation to
type.__new__. This requires cooperation from custom
metaclasses to ensure that the new __classcell__ entry
is passed along appropriately.

The initial implementation of that change resulted in abruptly
broken zero-argument super() support in metaclasses that didn't
adhere to the new requirements (such as Django's metaclass for
Model definitions).

The updated approach adopted here instead emits a deprecation
warning for those cases, and makes them work the same way they
did in Python 3.5.

This patch also improves the related class machinery documentation
to cover these details and to include more reader-friendly
cross-references and index entries.

a var-positional argument.  Added opcode BUILD_TUPLE_UNPACK_WITH_CALL.

The __class__ cell used by zero-argument super() is now initialized
from type.__new__ rather than __build_class__, so class methods
relying on that will now work correctly when called from metaclass
methods during class creation.

Patch by Martin Teichmann.

Issue #27213: Rework CALL_FUNCTION* opcodes to produce shorter and more
efficient bytecode:

* CALL_FUNCTION now only accepts position arguments
* CALL_FUNCTION_KW accepts position arguments and keyword arguments, but keys
  of keyword arguments are packed into a constant tuple.
* CALL_FUNCTION_EX is the most generic, it expects a tuple and a dict for
  positional and keyword arguments.

CALL_FUNCTION_VAR and CALL_FUNCTION_VAR_KW opcodes have been removed.

2 tests of test_traceback are currently broken: skip test, the issue #28050 was
created to track the issue.

Patch by Demur Rumed, design by Serhiy Storchaka, reviewed by Serhiy Storchaka
and Victor Stinner.

Patch by Ivan Levkivskyi.

Windows.

Originally only b'PYTHONCASEOK' was being checked for in os.environ,
but that won't work under Windows where all environment variables are
strings (on OS X they are bytes).

Thanks to Eryk Sun for the bug report.

Thanks to Oren Milman for the patch.

Patch by Demur Rumed.

function with generalized unpacking (PEP 448) and conflicting keyword names
could cause undefined behavior.

Patch by Demur Rumed.

Issue #26073: Updates magic number comment in _bootstrap_external.py and changes numbers in launcher.py to decimal to match official table.

Issue #26538: libregrtest: Fix setup_tests() to keep module.__path__ type
(_NamespacePath), don't convert to a list.

Add _NamespacePath.__setitem__() method to importlib._bootstrap_external.

to format short Python version.

Issue #26107: The format of the co_lnotab attribute of code objects changes to
support negative line number delta.

Changes:

* assemble_lnotab(): if line number delta is less than -128 or greater than
  127, emit multiple (offset_delta, lineno_delta) in co_lnotab
* update functions decoding co_lnotab to use signed 8-bit integers

  - dis.findlinestarts()
  - PyCode_Addr2Line()
  - _PyCode_CheckLineNumber()
  - frame_setlineno()

* update lnotab_notes.txt
* increase importlib MAGIC_NUMBER to 3361
* document the change in What's New in Python 3.6
* cleanup also PyCode_Optimize() to use better variable names