Typing improvements

While there is still a lot of work to do (mainly in Registry, Quantity, Unit),
this large PR makes several changes all around the code. There has not been
any intended functional change, but certain typing improvements required
code minor code refactoring to streamline input and output types of functions.

An important experimental idea is the PintScalar and PintArray protocols,
and Magnitude type. This is to overcome the lack of a proper numerical
hierarchy in Python.

1 files changed, 17 insertions, 16 deletions

diff --git a/pint/formatting.py b/pint/formatting.py
index dcc8725..637d838 100644
--- a/pint/formatting.py
+++ b/pint/formatting.py
@@ -13,7 +13,8 @@ from __future__ import annotations
 import functools
 import re
 import warnings
-from typing import Callable
+from typing import Callable, Iterable, Any
+from numbers import Number
 
 from .babel_names import _babel_lengths, _babel_units
 from .compat import babel_parse
@@ -21,7 +22,7 @@ from .compat import babel_parse
 __JOIN_REG_EXP = re.compile(r"{\d*}")
 
 
-def _join(fmt, iterable):
+def _join(fmt: str, iterable: Iterable[Any]):
     """Join an iterable with the format specified in fmt.
 
     The format can be specified in two ways:
@@ -55,7 +56,7 @@ def _join(fmt, iterable):
 _PRETTY_EXPONENTS = "⁰¹²³⁴⁵⁶⁷⁸⁹"
 
 
-def _pretty_fmt_exponent(num):
+def _pretty_fmt_exponent(num: Number) -> str:
     """Format an number into a pretty printed exponent.
 
     Parameters
@@ -76,7 +77,7 @@ def _pretty_fmt_exponent(num):
 
 #: _FORMATS maps format specifications to the corresponding argument set to
 #: formatter().
-_FORMATS: dict[str, dict] = {
+_FORMATS: dict[str, dict[str, Any]] = {
     "P": {  # Pretty format.
         "as_ratio": True,
         "single_denominator": False,
@@ -125,7 +126,7 @@ _FORMATS: dict[str, dict] = {
 _FORMATTERS: dict[str, Callable] = {}
 
 
-def register_unit_format(name):
+def register_unit_format(name: str):
     """register a function as a new format for units
 
     The registered function must have a signature of:
@@ -268,18 +269,18 @@ def format_compact(unit, registry, **options):
 
 
 def formatter(
-    items,
-    as_ratio=True,
-    single_denominator=False,
-    product_fmt=" * ",
-    division_fmt=" / ",
-    power_fmt="{} ** {}",
-    parentheses_fmt="({0})",
+    items: list[tuple[str, Number]],
+    as_ratio: bool = True,
+    single_denominator: bool = False,
+    product_fmt: str = " * ",
+    division_fmt: str = " / ",
+    power_fmt: str = "{} ** {}",
+    parentheses_fmt: str = "({0})",
     exp_call=lambda x: f"{x:n}",
-    locale=None,
-    babel_length="long",
-    babel_plural_form="one",
-    sort=True,
+    locale: str | None = None,
+    babel_length: str = "long",
+    babel_plural_form: str = "one",
+    sort: bool = True,
 ):
     """Format a list of (name, exponent) pairs.