October 2021
Python 3.10 was released on 4 October 2021, with Pablo Galindo Salgado as Release Manager. The release brings structural changes to the parser (new PEG parser, PEP 617, which arrived in 3.9) and weighty syntactic additions, including the most debated of the 3.x series: pattern matching.
Structural Pattern Matching (PEP 634-636)
The most visible novelty: match / case. Three coordinated PEPs (634 spec, 635 motivation, 636 tutorial). Syntactically inspired by OCaml/Haskell/Scala/Rust, with Pythonic adaptations:
def describe(point):
match point:
case (0, 0):
return "origin"
case (x, 0):
return f"on X axis (x={x})"
case (0, y):
return f"on Y axis (y={y})"
case (x, y):
return f"point ({x}, {y})"
case _:
return "unrecognised"Match is not a C-style switch/case — it is a destructuring pattern match supporting:
- Literal patterns —
case 42,case "done",case True - Capture patterns —
case xbinds - Sequence patterns —
case [a, b, *rest] - Mapping patterns —
case {"name": name, "age": age} - Class patterns —
case Point(x=0, y=y)— uses__match_args__ - OR patterns —
case 1 | 2 | 3 - Guard patterns —
case x if x > 0 - Wildcard —
case _
The mechanism integrates with existing protocols (e.g. __match_args__ on dataclass), making matching on complex structures natural.
Type Union syntax (PEP 604)
Another elegant syntax: X | Y replaces Union[X, Y] in type annotations.
# Before (still supported)
from typing import Union
def f(x: Union[int, str]) -> Union[int, None]: ...
# Python 3.10+
def f(x: int | str) -> int | None: ...The syntax mirrors | use in other typed languages (TypeScript, Kotlin) and makes annotations more readable.
Parenthesized context managers
The new PEG parser (PEP 617) enables multi-line syntax for with:
with (
open("input.txt") as fin,
open("output.txt", "w") as fout,
lock_resource() as resource,
):
# body
...Formatting multi-manager used to be awkward — required contextlib.ExitStack or backslash continuations. Now it is syntactically clean.
Improved error messages
The new PEG parser enables much more precise error messages:
# Python 3.9
File "foo.py", line 1
x = {'a': 1, 'b': 2, 'c': 3
^
SyntaxError: invalid syntax
# Python 3.10
File "foo.py", line 1
x = {'a': 1, 'b': 2, 'c': 3
^
SyntaxError: '{' was never closedErrors indicate cause and not just where the parser choked. Even NameError messages suggest “did you mean…?” for variables with typos.
Other typing contributions
- Explicit TypeAlias (PEP 613):
Vector: TypeAlias = list[float] - ParamSpec (PEP 612): typing of decorators preserving signature
- TypeGuard (PEP 647): explicit type narrowing for runtime checks
- Concatenate (PEP 612)
zip(strict=True)
zip() accepts strict=True to raise ValueError if iterables have different lengths — useful for debugging unexpected data.
Other novelties
- Distutils deprecated (removal in 3.12)
- async with contextlib.aclosing() (PEP 637)
- int.bit_count() — popcount
- dict union operators (consolidated from 3.9):
d1 | d2
Support and adoption
Python 3.10 has support through October 2026 (standard 5 years). Project adoption is relatively rapid:
- Black, mypy, ruff add support
- Django 4.0 (December 2021) supports 3.10
- FastAPI, Pydantic — full pattern matching support in examples and docs
Performance
Core optimisations:
- Inline constant literals
- Optimised store/load
- struct pack/unpack improved
Average benchmarks: 3-10% faster than 3.9 on typical workloads.
In the Italian context
Python 3.10 diffuses normally:
- Data science — rapid adoption
- Backend web — new projects on 3.10 from 2022
- PA — slower adoption policy; 3.8/3.9 remain dominant for a while
Structural pattern matching is welcomed with interest — similar to match in Rust/Scala, it shifts Python code style toward more functional forms for parsing and state machines.
References: Python 3.10.0 (4 October 2021). Pablo Galindo Salgado as Release Manager. PEP 634/635/636 (pattern matching), PEP 604 (union syntax), PEP 617 (PEG parser), PEP 613 (TypeAlias), PEP 612 (ParamSpec, Concatenate), PEP 647 (TypeGuard).