""" pint.util ~~~~~~~~~ Miscellaneous functions for pint. :copyright: 2016 by Pint Authors, see AUTHORS for more details. :license: BSD, see LICENSE for more details. """ from __future__ import annotations import logging import math import operator import re import tokenize import types from collections import deque from collections.abc import Callable, Generator, Hashable, Iterable, Iterator, Mapping from fractions import Fraction from functools import lru_cache, partial from logging import NullHandler from numbers import Number from token import NAME, NUMBER from typing import ( TYPE_CHECKING, Any, ClassVar, TypeAlias, TypeVar, ) from . import pint_eval from ._typing import Scalar from .compat import NUMERIC_TYPES, Self from .errors import DefinitionSyntaxError from .pint_eval import build_eval_tree if TYPE_CHECKING: from ._typing import QuantityOrUnitLike from .registry import UnitRegistry logger = logging.getLogger(__name__) logger.addHandler(NullHandler()) T = TypeVar("T") TH = TypeVar("TH", bound=Hashable) TT = TypeVar("TT", bound=type) ItMatrix: TypeAlias = Iterable[Iterable[Scalar]] Matrix: TypeAlias = list[list[Scalar]] def _noop(x: T) -> T: return x def matrix_to_string( matrix: ItMatrix, row_headers: Iterable[str] | None = None, col_headers: Iterable[str] | None = None, fmtfun: Callable[ [ Scalar, ], str, ] = "{:0.0f}".format, ) -> str: """Return a string representation of a matrix. Parameters ---------- matrix A matrix given as an iterable of an iterable of numbers. row_headers An iterable of strings to serve as row headers. (default = None, meaning no row headers are printed.) col_headers An iterable of strings to serve as column headers. (default = None, meaning no col headers are printed.) fmtfun A callable to convert a number into string. (default = `"{:0.0f}".format`) Returns ------- str String representation of the matrix. """ ret: list[str] = [] if col_headers: ret.append(("\t" if row_headers else "") + "\t".join(col_headers)) if row_headers: ret += [ rh + "\t" + "\t".join(fmtfun(f) for f in row) for rh, row in zip(row_headers, matrix) ] else: ret += ["\t".join(fmtfun(f) for f in row) for row in matrix] return "\n".join(ret) def transpose(matrix: ItMatrix) -> Matrix: """Return the transposed version of a matrix. Parameters ---------- matrix A matrix given as an iterable of an iterable of numbers. Returns ------- Matrix The transposed version of the matrix. """ return [list(val) for val in zip(*matrix)] def matrix_apply( matrix: ItMatrix, func: Callable[ [ Scalar, ], Scalar, ], ) -> Matrix: """Apply a function to individual elements within a matrix. Parameters ---------- matrix A matrix given as an iterable of an iterable of numbers. func A callable that converts a number to another. Returns ------- A new matrix in which each element has been replaced by new one. """ return [[func(x) for x in row] for row in matrix] def column_echelon_form( matrix: ItMatrix, ntype: type = Fraction, transpose_result: bool = False ) -> tuple[Matrix, Matrix, list[int]]: """Calculate the column echelon form using Gaussian elimination. Parameters ---------- matrix A 2D matrix as nested list. ntype The numerical type to use in the calculation. (default = Fraction) transpose_result Indicates if the returned matrix should be transposed. (default = False) Returns ------- ech_matrix Column echelon form. id_matrix Transformed identity matrix. swapped Swapped rows. """ _transpose: Callable[ [ ItMatrix, ], Matrix, ] = transpose if transpose_result else _noop ech_matrix = matrix_apply( transpose(matrix), lambda x: ntype.from_float(x) if isinstance(x, float) else ntype(x), # type: ignore ) rows, cols = len(ech_matrix), len(ech_matrix[0]) # M = [[ntype(x) for x in row] for row in M] id_matrix: list[list[Scalar]] = [ # noqa: E741 [ntype(1) if n == nc else ntype(0) for nc in range(rows)] for n in range(rows) ] swapped: list[int] = [] lead = 0 for r in range(rows): if lead >= cols: return _transpose(ech_matrix), _transpose(id_matrix), swapped s = r while ech_matrix[s][lead] == 0: # type: ignore s += 1 if s != rows: continue s = r lead += 1 if cols == lead: return _transpose(ech_matrix), _transpose(id_matrix), swapped ech_matrix[s], ech_matrix[r] = ech_matrix[r], ech_matrix[s] id_matrix[s], id_matrix[r] = id_matrix[r], id_matrix[s] swapped.append(s) lv = ech_matrix[r][lead] ech_matrix[r] = [mrx / lv for mrx in ech_matrix[r]] id_matrix[r] = [mrx / lv for mrx in id_matrix[r]] for s in range(rows): if s == r: continue lv = ech_matrix[s][lead] ech_matrix[s] = [ iv - lv * rv for rv, iv in zip(ech_matrix[r], ech_matrix[s]) ] id_matrix[s] = [iv - lv * rv for rv, iv in zip(id_matrix[r], id_matrix[s])] lead += 1 return _transpose(ech_matrix), _transpose(id_matrix), swapped def pi_theorem(quantities: dict[str, Any], registry: UnitRegistry | None = None): """Builds dimensionless quantities using the Buckingham π theorem Parameters ---------- quantities : dict mapping between variable name and units registry : (default value = None) Returns ------- type a list of dimensionless quantities expressed as dicts """ # Preprocess input and build the dimensionality Matrix quant = [] dimensions = set() if registry is None: getdim = _noop non_int_type = float else: getdim = registry.get_dimensionality non_int_type = registry.non_int_type for name, value in quantities.items(): if isinstance(value, str): value = ParserHelper.from_string(value, non_int_type=non_int_type) if isinstance(value, dict): dims = getdim(registry.UnitsContainer(value)) elif not hasattr(value, "dimensionality"): dims = getdim(value) else: dims = value.dimensionality if not registry and any(not key.startswith("[") for key in dims): logger.warning( "A non dimension was found and a registry was not provided. " "Assuming that it is a dimension name: {}.".format(dims) ) quant.append((name, dims)) dimensions = dimensions.union(dims.keys()) dimensions = list(dimensions) # Calculate dimensionless quantities matrix = [ [dimensionality[dimension] for name, dimensionality in quant] for dimension in dimensions ] ech_matrix, id_matrix, pivot = column_echelon_form(matrix, transpose_result=False) # Collect results # Make all numbers integers and minimize the number of negative exponents. # Remove zeros results = [] for rowm, rowi in zip(ech_matrix, id_matrix): if any(el != 0 for el in rowm): continue max_den = max(f.denominator for f in rowi) neg = -1 if sum(f < 0 for f in rowi) > sum(f > 0 for f in rowi) else 1 results.append( { q[0]: neg * f.numerator * max_den / f.denominator for q, f in zip(quant, rowi) if f.numerator != 0 } ) return results def solve_dependencies( dependencies: dict[TH, set[TH]], ) -> Generator[set[TH]]: """Solve a dependency graph. Parameters ---------- dependencies : dependency dictionary. For each key, the value is an iterable indicating its dependencies. Yields ------ set iterator of sets, each containing keys of independents tasks dependent only of the previous tasks in the list. Raises ------ ValueError if a cyclic dependency is found. """ while dependencies: # values not in keys (items without dep) t = {i for v in dependencies.values() for i in v} - dependencies.keys() # and keys without value (items without dep) t.update(k for k, v in dependencies.items() if not v) # can be done right away if not t: raise ValueError( "Cyclic dependencies exist among these items: {}".format( ", ".join(repr(x) for x in dependencies.items()) ) ) # and cleaned up dependencies = {k: v - t for k, v in dependencies.items() if v} yield t def find_shortest_path(graph: dict[TH, set[TH]], start: TH, end: TH): """Find shortest path between two nodes within a graph. Parameters ---------- graph A graph given as a mapping of nodes to a set of all connected nodes to it. start Starting node. end End node. Returns ------- list[TH] The shortest path between two nodes. """ path = [start] if start == end: return path fifo = deque() fifo.append((start, path)) visited = set() while fifo: node, path = fifo.popleft() visited.add(node) for adjascent_node in graph[node] - visited: if adjascent_node == end: return path + [adjascent_node] else: fifo.append((adjascent_node, path + [adjascent_node])) return None def find_connected_nodes( graph: dict[TH, set[TH]], start: TH, visited: set[TH] | None = None ) -> set[TH] | None: """Find all nodes connected to a start node within a graph. Parameters ---------- graph A graph given as a mapping of nodes to a set of all connected nodes to it. start Starting node. visited Mutable set to collect visited nodes. (default = None, empty set) Returns ------- set[TH] The shortest path between two nodes. """ # TODO: raise ValueError when start not in graph if start not in graph: return None visited = visited or set() visited.add(start) for node in graph[start]: if node not in visited: find_connected_nodes(graph, node, visited) return visited class udict(dict[str, Scalar]): """Custom dict implementing __missing__.""" def __missing__(self, key: str): return 0 def copy(self: Self) -> Self: return udict(self) class UnitsContainer(Mapping[str, Scalar]): """The UnitsContainer stores the product of units and their respective exponent and implements the corresponding operations. UnitsContainer is a read-only mapping. All operations (even in place ones) return new instances. Parameters ---------- non_int_type Numerical type used for non integer values. """ __slots__ = ("_d", "_hash", "_one", "_non_int_type") _d: udict _hash: int | None _one: Scalar _non_int_type: type def __init__( self, *args: Any, non_int_type: type | None = None, **kwargs: Any ) -> None: if args and isinstance(args[0], UnitsContainer): default_non_int_type = args[0]._non_int_type else: default_non_int_type = float self._non_int_type = non_int_type or default_non_int_type if self._non_int_type is float: self._one = 1 else: self._one = self._non_int_type("1") d = udict(*args, **kwargs) self._d = d for key, value in d.items(): if not isinstance(key, str): raise TypeError(f"key must be a str, not {type(key)}") if not isinstance(value, Number): raise TypeError(f"value must be a number, not {type(value)}") if not isinstance(value, int) and not isinstance(value, self._non_int_type): d[key] = self._non_int_type(value) self._hash = None def copy(self: Self) -> Self: """Create a copy of this UnitsContainer.""" return self.__copy__() def add(self: Self, key: str, value: Number) -> Self: """Create a new UnitsContainer adding value to the value existing for a given key. Parameters ---------- key unit to which the value will be added. value value to be added. Returns ------- UnitsContainer A copy of this container. """ newval = self._d[key] + self._normalize_nonfloat_value(value) new = self.copy() if newval: new._d[key] = newval else: new._d.pop(key) new._hash = None return new def remove(self: Self, keys: Iterable[str]) -> Self: """Create a new UnitsContainer purged from given entries. Parameters ---------- keys Iterable of keys (units) to remove. Returns ------- UnitsContainer A copy of this container. """ new = self.copy() for k in keys: new._d.pop(k) new._hash = None return new def rename(self: Self, oldkey: str, newkey: str) -> Self: """Create a new UnitsContainer in which an entry has been renamed. Parameters ---------- oldkey Existing key (unit). newkey New key (unit). Returns ------- UnitsContainer A copy of this container. """ new = self.copy() new._d[newkey] = new._d.pop(oldkey) new._hash = None return new def unit_items(self) -> Iterable[tuple[str, Scalar]]: return self._d.items() def __iter__(self) -> Iterator[str]: return iter(self._d) def __len__(self) -> int: return len(self._d) def __getitem__(self, key: str) -> Scalar: return self._d[key] def __contains__(self, key: str) -> bool: return key in self._d def __hash__(self) -> int: if self._hash is None: self._hash = hash(frozenset(self._d.items())) return self._hash # Only needed by pickle protocol 0 and 1 (used by pytables) def __getstate__(self) -> tuple[udict, Scalar, type]: return self._d, self._one, self._non_int_type def __setstate__(self, state: tuple[udict, Scalar, type]): self._d, self._one, self._non_int_type = state self._hash = None def __eq__(self, other: Any) -> bool: if isinstance(other, UnitsContainer): # UnitsContainer.__hash__(self) is not the same as hash(self); see # ParserHelper.__hash__ and __eq__. # Different hashes guarantee that the actual contents are different, but # identical hashes give no guarantee of equality. # e.g. in CPython, hash(-1) == hash(-2) if UnitsContainer.__hash__(self) != UnitsContainer.__hash__(other): return False other = other._d elif isinstance(other, str): try: other = ParserHelper.from_string(other, self._non_int_type) except DefinitionSyntaxError: return False other = other._d return dict.__eq__(self._d, other) def __str__(self) -> str: return self.__format__("") def __repr__(self) -> str: tmp = "{%s}" % ", ".join( [f"'{key}': {value}" for key, value in sorted(self._d.items())] ) return f"" def __format__(self, spec: str) -> str: # TODO: provisional from .formatting import format_unit return format_unit(self, spec) def format_babel(self, spec: str, registry=None, **kwspec) -> str: # TODO: provisional from .formatting import format_unit return format_unit(self, spec, registry=registry, **kwspec) def __copy__(self): # Skip expensive health checks performed by __init__ out = object.__new__(self.__class__) out._d = self._d.copy() out._hash = self._hash out._non_int_type = self._non_int_type out._one = self._one return out def __mul__(self, other: Any): if not isinstance(other, self.__class__): err = "Cannot multiply UnitsContainer by {}" raise TypeError(err.format(type(other))) new = self.copy() for key, value in other.items(): new._d[key] += value if new._d[key] == 0: del new._d[key] new._hash = None return new __rmul__ = __mul__ def __pow__(self, other: Any): if not isinstance(other, NUMERIC_TYPES): err = "Cannot power UnitsContainer by {}" raise TypeError(err.format(type(other))) new = self.copy() for key, value in new._d.items(): new._d[key] *= other new._hash = None return new def __truediv__(self, other: Any): if not isinstance(other, self.__class__): err = "Cannot divide UnitsContainer by {}" raise TypeError(err.format(type(other))) new = self.copy() for key, value in other.items(): new._d[key] -= self._normalize_nonfloat_value(value) if new._d[key] == 0: del new._d[key] new._hash = None return new def __rtruediv__(self, other: Any): if not isinstance(other, self.__class__) and other != 1: err = "Cannot divide {} by UnitsContainer" raise TypeError(err.format(type(other))) return self**-1 def _normalize_nonfloat_value(self, value: Scalar) -> Scalar: if not isinstance(value, int) and not isinstance(value, self._non_int_type): return self._non_int_type(value) # type: ignore[no-any-return] return value class ParserHelper(UnitsContainer): """The ParserHelper stores in place the product of variables and their respective exponent and implements the corresponding operations. It also provides a scaling factor. For example: `3 * m ** 2` becomes ParserHelper(3, m=2) Briefly is a UnitsContainer with a scaling factor. ParserHelper is a read-only mapping. All operations (even in place ones) return new instances. WARNING : The hash value used does not take into account the scale attribute so be careful if you use it as a dict key and then two unequal object can have the same hash. Parameters ---------- scale Scaling factor. (default = 1) **kwargs Used to populate the dict of units and exponents. """ __slots__ = ("scale",) scale: Scalar def __init__(self, scale: Scalar = 1, *args, **kwargs): super().__init__(*args, **kwargs) self.scale = scale @classmethod def from_word(cls, input_word: str, non_int_type: type = float) -> ParserHelper: """Creates a ParserHelper object with a single variable with exponent one. Equivalent to: ParserHelper(1, {input_word: 1}) Parameters ---------- input_word non_int_type Numerical type used for non integer values. """ if non_int_type is float: return cls(1, [(input_word, 1)], non_int_type=non_int_type) else: ONE = non_int_type("1") return cls(ONE, [(input_word, ONE)], non_int_type=non_int_type) @classmethod def eval_token(cls, token: tokenize.TokenInfo, non_int_type: type = float): token_type = token.type token_text = token.string if token_type == NUMBER: if non_int_type is float: try: return int(token_text) except ValueError: return float(token_text) else: return non_int_type(token_text) elif token_type == NAME: return ParserHelper.from_word(token_text, non_int_type=non_int_type) else: raise Exception("unknown token type") @classmethod @lru_cache def from_string(cls, input_string: str, non_int_type: type = float) -> ParserHelper: """Parse linear expression mathematical units and return a quantity object. Parameters ---------- input_string non_int_type Numerical type used for non integer values. """ if not input_string: return cls(non_int_type=non_int_type) input_string = string_preprocessor(input_string) if "[" in input_string: input_string = input_string.replace("[", "__obra__").replace( "]", "__cbra__" ) reps = True else: reps = False gen = pint_eval.tokenizer(input_string) ret = build_eval_tree(gen).evaluate( partial(cls.eval_token, non_int_type=non_int_type) ) if isinstance(ret, Number): return cls(ret, non_int_type=non_int_type) if reps: ret = cls( ret.scale, { key.replace("__obra__", "[").replace("__cbra__", "]"): value for key, value in ret.items() }, non_int_type=non_int_type, ) for k in list(ret): if k.lower() == "nan": del ret._d[k] ret.scale = non_int_type(math.nan) return ret def __copy__(self): new = super().__copy__() new.scale = self.scale return new def copy(self): return self.__copy__() def __hash__(self): if self.scale != 1: mess = "Only scale 1 ParserHelper instance should be considered hashable" raise ValueError(mess) return super().__hash__() # Only needed by pickle protocol 0 and 1 (used by pytables) def __getstate__(self): return super().__getstate__() + (self.scale,) def __setstate__(self, state): super().__setstate__(state[:-1]) self.scale = state[-1] def __eq__(self, other: Any) -> bool: if isinstance(other, ParserHelper): return self.scale == other.scale and super().__eq__(other) elif isinstance(other, str): return self == ParserHelper.from_string(other, self._non_int_type) elif isinstance(other, Number): return self.scale == other and not len(self._d) return self.scale == 1 and super().__eq__(other) def operate(self, items, op=operator.iadd, cleanup: bool = True): d = udict(self._d) for key, value in items: d[key] = op(d[key], value) if cleanup: keys = [key for key, value in d.items() if value == 0] for key in keys: del d[key] return self.__class__(self.scale, d, non_int_type=self._non_int_type) def __str__(self): tmp = "{%s}" % ", ".join( [f"'{key}': {value}" for key, value in sorted(self._d.items())] ) return f"{self.scale} {tmp}" def __repr__(self): tmp = "{%s}" % ", ".join( [f"'{key}': {value}" for key, value in sorted(self._d.items())] ) return f"" def __mul__(self, other): if isinstance(other, str): new = self.add(other, self._one) elif isinstance(other, Number): new = self.copy() new.scale *= other elif isinstance(other, self.__class__): new = self.operate(other.items()) new.scale *= other.scale else: new = self.operate(other.items()) return new __rmul__ = __mul__ def __pow__(self, other): d = self._d.copy() for key in self._d: d[key] *= other return self.__class__(self.scale**other, d, non_int_type=self._non_int_type) def __truediv__(self, other): if isinstance(other, str): new = self.add(other, -1) elif isinstance(other, Number): new = self.copy() new.scale /= other elif isinstance(other, self.__class__): new = self.operate(other.items(), operator.sub) new.scale /= other.scale else: new = self.operate(other.items(), operator.sub) return new __floordiv__ = __truediv__ def __rtruediv__(self, other): new = self.__pow__(-1) if isinstance(other, str): new = new.add(other, self._one) elif isinstance(other, Number): new.scale *= other elif isinstance(other, self.__class__): new = self.operate(other.items(), operator.add) new.scale *= other.scale else: new = new.operate(other.items(), operator.add) return new #: List of regex substitution pairs. _subs_re_list = [ ("\N{DEGREE SIGN}", "degree"), (r"([\w\.\-\+\*\\\^])\s+", r"\1 "), # merge multiple spaces (r"({}) squared", r"\1**2"), # Handle square and cube (r"({}) cubed", r"\1**3"), (r"cubic ({})", r"\1**3"), (r"square ({})", r"\1**2"), (r"sq ({})", r"\1**2"), ( r"\b([0-9]+\.?[0-9]*)(?=[e|E][a-zA-Z]|[a-df-zA-DF-Z])", r"\1*", ), # Handle numberLetter for multiplication (r"([\w\.\)])\s+(?=[\w\(])", r"\1*"), # Handle space for multiplication ] #: Compiles the regex and replace {} by a regex that matches an identifier. _subs_re = [ (re.compile(a.format(r"[_a-zA-Z][_a-zA-Z0-9]*")), b) for a, b in _subs_re_list ] _pretty_table = str.maketrans("⁰¹²³⁴⁵⁶⁷⁸⁹·⁻", "0123456789*-") _pretty_exp_re = re.compile(r"(⁻?[⁰¹²³⁴⁵⁶⁷⁸⁹]+(?:\.[⁰¹²³⁴⁵⁶⁷⁸⁹]*)?)") def string_preprocessor(input_string: str) -> str: input_string = input_string.replace(",", "") input_string = input_string.replace(" per ", "/") for a, b in _subs_re: input_string = a.sub(b, input_string) input_string = _pretty_exp_re.sub(r"**(\1)", input_string) # Replace pretty format characters input_string = input_string.translate(_pretty_table) # Handle caret exponentiation input_string = input_string.replace("^", "**") return input_string def _is_dim(name: str) -> bool: return name[0] == "[" and name[-1] == "]" class SharedRegistryObject: """Base class for object keeping a reference to the registree. Such object are for now Quantity and Unit, in a number of places it is that an object from this class has a '_units' attribute. Parameters ---------- Returns ------- """ _REGISTRY: ClassVar[UnitRegistry] _units: UnitsContainer def __new__(cls, *args, **kwargs): inst = object.__new__(cls) if not hasattr(cls, "_REGISTRY"): # Base class, not subclasses dynamically by # UnitRegistry._init_dynamic_classes from . import application_registry inst._REGISTRY = application_registry.get() return inst def _check(self, other: Any) -> bool: """Check if the other object use a registry and if so that it is the same registry. Parameters ---------- other Returns ------- bool Raises ------ ValueError if other don't use the same unit registry. """ if self._REGISTRY is getattr(other, "_REGISTRY", None): return True elif isinstance(other, SharedRegistryObject): mess = "Cannot operate with {} and {} of different registries." raise ValueError( mess.format(self.__class__.__name__, other.__class__.__name__) ) else: return False class PrettyIPython: """Mixin to add pretty-printers for IPython""" default_format: str def _repr_html_(self) -> str: if "~" in self._REGISTRY.formatter.default_format: return f"{self:~H}" return f"{self:H}" def _repr_latex_(self) -> str: if "~" in self._REGISTRY.formatter.default_format: return f"${self:~L}$" return f"${self:L}$" def _repr_pretty_(self, p, cycle: bool): # if cycle: if "~" in self._REGISTRY.formatter.default_format: p.text(f"{self:~P}") else: p.text(f"{self:P}") # else: # p.pretty(self.magnitude) # p.text(" ") # p.pretty(self.units) def to_units_container( unit_like: QuantityOrUnitLike, registry: UnitRegistry | None = None ) -> UnitsContainer: """Convert a unit compatible type to a UnitsContainer. Parameters ---------- unit_like Quantity or Unit to infer the plain units from. registry If provided, uses the registry's UnitsContainer and parse_unit_name. If None, uses the registry attached to unit_like. Returns ------- UnitsContainer """ mro = type(unit_like).mro() if UnitsContainer in mro: return unit_like elif SharedRegistryObject in mro: return unit_like._units elif str in mro: if registry: # TODO: document how to whether to lift preprocessing loop out to caller for p in registry.preprocessors: unit_like = p(unit_like) return registry.parse_units_as_container(unit_like) else: return ParserHelper.from_string(unit_like) elif dict in mro: if registry: return registry.UnitsContainer(unit_like) else: return UnitsContainer(unit_like) def infer_base_unit( unit_like: QuantityOrUnitLike, registry: UnitRegistry | None = None ) -> UnitsContainer: """ Given a Quantity or UnitLike, give the UnitsContainer for it's plain units. Parameters ---------- unit_like Quantity or Unit to infer the plain units from. registry If provided, uses the registry's UnitsContainer and parse_unit_name. If None, uses the registry attached to unit_like. Returns ------- UnitsContainer Raises ------ ValueError The unit_like did not reference a registry, and no registry was provided. """ d = udict() original_units = to_units_container(unit_like, registry) if registry is None and hasattr(unit_like, "_REGISTRY"): registry = unit_like._REGISTRY if registry is None: raise ValueError("No registry provided.") for unit_name, power in original_units.items(): candidates = registry.parse_unit_name(unit_name) assert len(candidates) == 1 _, base_unit, _ = candidates[0] d[base_unit] += power # remove values that resulted in a power of 0 nonzero_dict = {k: v for k, v in d.items() if v != 0} return registry.UnitsContainer(nonzero_dict) def getattr_maybe_raise(obj: Any, item: str): """Helper function invoked at start of all overridden ``__getattr__``. Raise AttributeError if the user tries to ask for a _ or __ attribute, *unless* it is immediately followed by a number, to enable units encompassing constants, such as ``L / _100km``. Parameters ---------- item attribute to be found. Raises ------ AttributeError """ # Double-underscore attributes are tricky to detect because they are # automatically prefixed with the class name - which may be a subclass of obj if ( item.endswith("__") or len(item.lstrip("_")) == 0 or (item.startswith("_") and not item.lstrip("_")[0].isdigit()) ): raise AttributeError(f"{obj!r} object has no attribute {item!r}") def iterable(y: Any) -> bool: """Check whether or not an object can be iterated over.""" try: iter(y) except TypeError: return False return True def sized(y: Any) -> bool: """Check whether or not an object has a defined length.""" try: len(y) except TypeError: return False return True def create_class_with_registry( registry: UnitRegistry, base_class: type[TT] ) -> type[TT]: """Create new class inheriting from base_class and filling _REGISTRY class attribute with an actual instanced registry. """ class_body = { "__module__": "pint", "_REGISTRY": registry, } return types.new_class( base_class.__name__, bases=(base_class,), exec_body=lambda ns: ns.update(class_body), )