[Study] Python 3.7 Spec

New syntax features:
- PEP 563, postponed evaluation of type annotations.
Backwards incompatible syntax changes:
- async and await are now reserved keywords.
New library modules:
- contextvars: PEP 567 – Context Variables
- dataclasses: PEP 557 – Data Classes
- importlib.resources
New built-in features:
- PEP 553, the new breakpoint() function.
Python data model improvements:
- PEP 562, customization of access to module attributes.
- PEP 560, core support for typing module and generic types.

the insertion-order preservation nature of dict objects has been declared to be an official part of the Python language spec.

Significant improvements in the standard library:

The asyncio module has received new features, significant usability and performance improvements.

The time module gained support for functions with nanosecond resolution.

CPython implementation improvements:

Avoiding the use of ASCII as a default text encoding:

PEP 538, legacy C locale coercion

PEP 540, forced UTF-8 runtime mode

PEP 552, deterministic .pycs

the new development runtime mode

PEP 565, improved DeprecationWarning handling

C API improvements:

PEP 539, new C API for thread-local storage

Documentation improvements:

PEP 545, Python documentation translations

New documentation translations: Japanese, French, and Korean.

This release features notable performance improvements in many areas. The Optimizations section lists them in detail.

For a list of changes that may affect compatibility with previous Python releases please refer to the Porting to Python 3.7 section.

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