Python version history comparison today. Scraped the releases and decided what version to run my apps on, and what new features to add to them.

3.0 (2008-12-03)

• print statement -> function
• dict.iteritems() -> dict.items()
• raw_input() -> input()
• many things return iterators instead of lists (zip, map, keys, etc)
• unicode string no longer necessary, assumes it
• string formatting, starting to deprecate % and use format
• using with for context management

3.1 (2009-06-27)

• collections.OrderedDict added
• collections.Counter added
• unittest can be marked skip and expectedFailure
• .format() can automatically add commas in the thousands places

3.2 (2011-02-20)

• Stable ABI (easier to write extensions across versions)
• argparse replaced optparse, which only had support for positional args
• logging config by json file
• concurrent.futures for thread/process management
• pyc moved to __pycache__
• wsgi headers need to be native strings, no encoding
• @functools.lru_cache added
• itertools.accumulate() added
• contextlib now allows contextmanagers to be used as function decorators as well
• can now use a .pdbrc

3.3 (2012-09-29)

• added venv as a stdlib module, for programmatic access from python, as well as command line access via pyvenv (and then python -m venv)
• added mock to unittest in stdlib
• added py launcher for windows (double clicking .py automatically runs them)
• yield from to delegate generators
• __qualname__ for fully qualified path to that object

3.4 (2014-03-16)

• asyncio added
• enum added
• pathlib added
• statistics added
• tracemalloc added
• pip is shipped with python now, always

3.5 (2015-09-13)

• typing (could use comments and annotation before, but this formalizes)
• coroutines can be used with async / await syntax (diff syntax before)
• can multiply matrices with A @ B instead of dot(A, B)
• much of stdlib reimplemented in C, improving perf significantly
• os.scandir() added (better than the os.walk function)
• math.inf and math.nan constants were added

3.6 (2016-12-23)

• f strings
• dicts use 25% less mem
• underscores in numbers
• async generators and async comprehensions
• typing for variable annotations
• secrets module added to stdlib
• asyncio was introduced in 3.4 as provisional but is now declared stable

3.7 (2018-06-27)

• types now have postponed evaluation; basically annotations allow hoisting
• breakpoint() added (internally, this calls sys.breakpointhook(), which calls pdb.set_trace())
• the time module now supports nanoseconds (for most functions)
• typing was introduced in 3.5 as provisional but is now declared stable
• added dataclasses

3.8 (2019-10-14)

• walrus operator
• / in function param means it MUST be positional (can’t be keyword)
• using = in an fstring will insert not just the value of the var but also the name of the var (really helpful for printing and debugging)
• async mocks were added to unittest

3.9 (2020-10-05)

• dict merge | (same as {**d1, **d2}) and update |= (same as dict.update) operators
• graphlib added to stdlib

3.10 (2021-10-04)

• much better error messages in standard exceptions (more specific syntax)
• structural pattern matching (switch statements!)
• type union operator: you can do int | float instead of Union[int, float]
• distutils is deprecated, and will be removed in 3.12 (just setuptools now)

3.11 (2022-10-24)

• all around 10-60% faster, average 1.25x, uses slightly more mem tho
• added tomllib, can parse toml now with stdlib
• even more specificity in tracebacks, pointing to exact problem
• multiple exceptions can be raised simultaneously in groups
• ton of deprecated stdlib modules and functions removed (none that I really use)