Python - what is new in which version?

Coroutines can now be defined with async keyword and awaited with await keyword. These keywords are not reserved yet. They will be become proper reserved keywords in Python 3.7.

async can also be used in async for and async with statements for asynchronous for loops and context managers.

typing module adds support for Type Hints (PEP484). While syntax for function annotation was introduced back in Python3.0 (PEP3107, this module provides some standard tools (such as types Any, Union, Tuple, Callable, etc.) that can be used in type annotations.

zipapp provides tools to manage the creation of zip files containing Python code, which can be executed directly by the Python interpreter.

collections.OrderedDict is significantly faster now.

os.scandir() is a new function for better and faster way of directory traversal.

Formatted string literals (f-strings). Defined in PEP498.

Support for variable type hints (PEP526).

Underscores in numeric literals: 1_000_000 (PEP515).

Asynchronous generators (PEP525) and comprehensions (PEP530).

secrets for generating cryptographically strong random numbers suitable for managing data such as passwords, account authentication, security tokens, and related secrets. Described in PEP506.

The new implementation of dictionaries is 20% to 25% more compact and preserves insertion order (but this should not be relied upon yet). See this great talk by Raymond Hettinger in which he explains how dictionaries changed over time.

asyncio is no longer provisional and the API is considered stable.

A new file system path protocol was added to support path-like object.

The datetime module has gained support for Local Time Disambiguation.

json.load() and json.loads() now support binary input.

A new function random.choices() returns a list of specified size with elements from a population with optional weights.

Class unittest.mock.Mock has new methods assert_called and assert_called_once.

Postponed evaluation of type annotations (PEP526).

async and await are now reserved keywords.

dataclasses provides a decorator and functions for automatically adding generated special methods such as __init__() and __repr__() to user-defined classes. It is useful when you need to create a simple class that only holds data but has no behavior.

breakpoint() function for debuggers.

Dictionaries now officially preserve insertion order of elements.

asyncio received a lot of new features and improvements (high-level asyncio.run() function for running coroutines, many others).

time module now has support for nanosecond resolution.

Debian 8, Ubuntu 16, CentOS 7.5 and other platforms that use OpenSSL 0.9.8 and 1.0.1 are no longer supported. At least OpenSSL 1.0.2 is required. You can build Python3.7 on those platforms but you have to manually link a new OpenSSL version.

Assignment expressions (the "walrus operator", :=):

Positional only arguments: There is new syntax (/) to indicate that some function parameters must be specified positionally.

This is in addition to keyword only arguments.

json.tool has a new option (--json-lines) to parse every input line as separate JSON object.

New class unittest.mock.AsyncMock for asynchronous mocking.