156 lines
4.0 KiB
Python
156 lines
4.0 KiB
Python
# SPDX-License-Identifier: MIT
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import functools
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import types
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from ._make import _make_ne
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_operation_names = {"eq": "==", "lt": "<", "le": "<=", "gt": ">", "ge": ">="}
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def cmp_using(
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eq=None,
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lt=None,
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le=None,
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gt=None,
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ge=None,
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require_same_type=True,
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class_name="Comparable",
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):
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"""
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Create a class that can be passed into `attr.ib`'s ``eq``, ``order``, and
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``cmp`` arguments to customize field comparison.
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The resulting class will have a full set of ordering methods if
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at least one of ``{lt, le, gt, ge}`` and ``eq`` are provided.
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:param Optional[callable] eq: `callable` used to evaluate equality
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of two objects.
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:param Optional[callable] lt: `callable` used to evaluate whether
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one object is less than another object.
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:param Optional[callable] le: `callable` used to evaluate whether
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one object is less than or equal to another object.
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:param Optional[callable] gt: `callable` used to evaluate whether
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one object is greater than another object.
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:param Optional[callable] ge: `callable` used to evaluate whether
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one object is greater than or equal to another object.
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:param bool require_same_type: When `True`, equality and ordering methods
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will return `NotImplemented` if objects are not of the same type.
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:param Optional[str] class_name: Name of class. Defaults to 'Comparable'.
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See `comparison` for more details.
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.. versionadded:: 21.1.0
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"""
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body = {
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"__slots__": ["value"],
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"__init__": _make_init(),
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"_requirements": [],
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"_is_comparable_to": _is_comparable_to,
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}
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# Add operations.
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num_order_functions = 0
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has_eq_function = False
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if eq is not None:
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has_eq_function = True
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body["__eq__"] = _make_operator("eq", eq)
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body["__ne__"] = _make_ne()
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if lt is not None:
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num_order_functions += 1
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body["__lt__"] = _make_operator("lt", lt)
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if le is not None:
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num_order_functions += 1
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body["__le__"] = _make_operator("le", le)
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if gt is not None:
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num_order_functions += 1
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body["__gt__"] = _make_operator("gt", gt)
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if ge is not None:
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num_order_functions += 1
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body["__ge__"] = _make_operator("ge", ge)
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type_ = types.new_class(
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class_name, (object,), {}, lambda ns: ns.update(body)
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)
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# Add same type requirement.
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if require_same_type:
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type_._requirements.append(_check_same_type)
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# Add total ordering if at least one operation was defined.
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if 0 < num_order_functions < 4:
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if not has_eq_function:
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# functools.total_ordering requires __eq__ to be defined,
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# so raise early error here to keep a nice stack.
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raise ValueError(
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"eq must be define is order to complete ordering from "
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"lt, le, gt, ge."
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)
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type_ = functools.total_ordering(type_)
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return type_
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def _make_init():
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"""
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Create __init__ method.
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"""
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def __init__(self, value):
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"""
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Initialize object with *value*.
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"""
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self.value = value
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return __init__
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def _make_operator(name, func):
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"""
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Create operator method.
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"""
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def method(self, other):
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if not self._is_comparable_to(other):
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return NotImplemented
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result = func(self.value, other.value)
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if result is NotImplemented:
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return NotImplemented
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return result
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method.__name__ = "__%s__" % (name,)
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method.__doc__ = "Return a %s b. Computed by attrs." % (
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_operation_names[name],
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)
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return method
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def _is_comparable_to(self, other):
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"""
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Check whether `other` is comparable to `self`.
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"""
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for func in self._requirements:
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if not func(self, other):
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return False
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return True
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def _check_same_type(self, other):
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"""
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Return True if *self* and *other* are of the same type, False otherwise.
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"""
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return other.value.__class__ is self.value.__class__
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