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