mirror of https://github.com/python/cpython
Remove references to __cmp__.
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@ -246,8 +246,8 @@ Glossary
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hashable
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An object is *hashable* if it has a hash value which never changes during
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its lifetime (it needs a :meth:`__hash__` method), and can be compared to
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other objects (it needs an :meth:`__eq__` or :meth:`__cmp__` method).
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Hashable objects which compare equal must have the same hash value.
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other objects (it needs an :meth:`__eq__` method). Hashable objects which
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compare equal must have the same hash value.
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Hashability makes an object usable as a dictionary key and a set member,
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because these data structures use the hash value internally.
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@ -375,15 +375,14 @@ Decimal objects
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.. method:: compare(other[, context])
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Compare the values of two Decimal instances. This operation behaves in
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the same way as the usual comparison method :meth:`__cmp__`, except that
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:meth:`compare` returns a Decimal instance rather than an integer, and if
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either operand is a NaN then the result is a NaN::
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Compare the values of two Decimal instances. :meth:`compare` returns a
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Decimal instance, and if either operand is a NaN then the result is a
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NaN::
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a or b is a NaN ==> Decimal('NaN')
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a < b ==> Decimal('-1')
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a == b ==> Decimal('0')
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a > b ==> Decimal('1')
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a or b is a NaN ==> Decimal('NaN')
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a < b ==> Decimal('-1')
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a == b ==> Decimal('0')
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a > b ==> Decimal('1')
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.. method:: compare_signal(other[, context])
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@ -173,7 +173,6 @@ any operand is a complex number, the objects are of different types that cannot
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be compared, or other cases where there is no defined ordering.
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.. index::
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single: __cmp__() (instance method)
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single: __eq__() (instance method)
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single: __ne__() (instance method)
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single: __lt__() (instance method)
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@ -181,15 +180,14 @@ be compared, or other cases where there is no defined ordering.
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single: __gt__() (instance method)
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single: __ge__() (instance method)
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Instances of a class normally compare as non-equal unless the class defines the
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:meth:`__eq__` or :meth:`__cmp__` method.
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Non-identical instances of a class normally compare as non-equal unless the
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class defines the :meth:`__eq__` method.
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Instances of a class cannot be ordered with respect to other instances of the
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same class, or other types of object, unless the class defines enough of the
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methods :meth:`__cmp__`, :meth:`__lt__`, :meth:`__le__`, :meth:`__gt__`, and
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:meth:`__ge__` (in general, either :meth:`__cmp__` or both :meth:`__lt__` and
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:meth:`__eq__` are sufficient, if you want the conventional meanings of the
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comparison operators).
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methods :meth:`__lt__`, :meth:`__le__`, :meth:`__gt__`, and :meth:`__ge__` (in
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general, :meth:`__lt__` and :meth:`__eq__` are sufficient, if you want the
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conventional meanings of the comparison operators).
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The behavior of the :keyword:`is` and :keyword:`is not` operators cannot be
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customized; also they can be applied to any two objects and never raise an
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@ -1642,8 +1640,7 @@ The constructors for both classes work the same:
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The subset and equality comparisons do not generalize to a complete ordering
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function. For example, any two disjoint sets are not equal and are not
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subsets of each other, so *all* of the following return ``False``: ``a<b``,
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``a==b``, or ``a>b``. Accordingly, sets do not implement the :meth:`__cmp__`
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method.
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``a==b``, or ``a>b``.
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Since sets only define partial ordering (subset relationships), the output of
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the :meth:`list.sort` method is undefined for lists of sets.
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@ -210,7 +210,7 @@ use by the marshalling/unmarshalling code:
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Write the XML-RPC encoding of this :class:`DateTime` item to the *out* stream
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object.
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It also supports certain of Python's built-in operators through :meth:`__cmp__`
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It also supports certain of Python's built-in operators through rich comparison
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and :meth:`__repr__` methods.
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A working example follows. The server code::
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@ -273,8 +273,8 @@ internal use by the marshalling/unmarshalling code:
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which was the de facto standard base64 specification when the
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XML-RPC spec was written.
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It also supports certain of Python's built-in operators through a
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:meth:`__cmp__` method.
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It also supports certain of Python's built-in operators through :meth:`__eq__`
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and :meth:`__ne__` methods.
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Example usage of the binary objects. We're going to transfer an image over
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XMLRPC::
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@ -1168,8 +1168,7 @@ Basic customization
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.. index::
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single: comparisons
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These are the so-called "rich comparison" methods, and are called for comparison
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operators in preference to :meth:`__cmp__` below. The correspondence between
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These are the so-called "rich comparison" methods. The correspondence between
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operator symbols and method names is as follows: ``x<y`` calls ``x.__lt__(y)``,
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``x<=y`` calls ``x.__le__(y)``, ``x==y`` calls ``x.__eq__(y)``, ``x!=y`` calls
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``x.__ne__(y)``, ``x>y`` calls ``x.__gt__(y)``, and ``x>=y`` calls
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@ -1198,28 +1197,11 @@ Basic customization
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Arguments to rich comparison methods are never coerced.
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.. method:: object.__cmp__(self, other)
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.. index::
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builtin: cmp
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single: comparisons
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Called by comparison operations if rich comparison (see above) is not
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defined. Should return a negative integer if ``self < other``, zero if
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``self == other``, a positive integer if ``self > other``. If no
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:meth:`__cmp__`, :meth:`__eq__` or :meth:`__ne__` operation is defined, class
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instances are compared by object identity ("address"). See also the
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description of :meth:`__hash__` for some important notes on creating
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:term:`hashable` objects which support custom comparison operations and are
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usable as dictionary keys.
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.. method:: object.__hash__(self)
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.. index::
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object: dictionary
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builtin: hash
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single: __cmp__() (object method)
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Called for the key object for dictionary operations, and by the built-in
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function :func:`hash`. Should return an integer usable as a hash value
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@ -1228,37 +1210,35 @@ Basic customization
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(e.g., using exclusive or) the hash values for the components of the object that
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also play a part in comparison of objects.
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If a class does not define a :meth:`__cmp__` or :meth:`__eq__` method it
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should not define a :meth:`__hash__` operation either; if it defines
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:meth:`__cmp__` or :meth:`__eq__` but not :meth:`__hash__`, its instances
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will not be usable as dictionary keys. If a class defines mutable objects
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and implements a :meth:`__cmp__` or :meth:`__eq__` method, it should not
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implement :meth:`__hash__`, since the dictionary implementation requires that
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a key's hash value is immutable (if the object's hash value changes, it will
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be in the wrong hash bucket).
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If a class does not define an :meth:`__eq__` method it should not define a
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:meth:`__hash__` operation either; if it defines :meth:`__eq__` but not
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:meth:`__hash__`, its instances will not be usable as dictionary keys. If a
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class defines mutable objects and implements an :meth:`__eq__` method, it
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should not implement :meth:`__hash__`, since the dictionary implementation
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requires that a key's hash value is immutable (if the object's hash value
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changes, it will be in the wrong hash bucket).
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User-defined classes have :meth:`__cmp__` and :meth:`__hash__` methods
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User-defined classes have :meth:`__eq__` and :meth:`__hash__` methods
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by default; with them, all objects compare unequal (except with themselves)
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and ``x.__hash__()`` returns ``id(x)``.
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Classes which inherit a :meth:`__hash__` method from a parent class but
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change the meaning of :meth:`__cmp__` or :meth:`__eq__` such that the hash
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value returned is no longer appropriate (e.g. by switching to a value-based
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concept of equality instead of the default identity based equality) can
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explicitly flag themselves as being unhashable by setting
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``__hash__ = None`` in the class definition. Doing so means that not only
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will instances of the class raise an appropriate :exc:`TypeError` when
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a program attempts to retrieve their hash value, but they will also be
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correctly identified as unhashable when checking
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``isinstance(obj, collections.Hashable)`` (unlike classes which define
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their own :meth:`__hash__` to explicitly raise :exc:`TypeError`).
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change the meaning of :meth:`__eq__` such that the hash value returned is no
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longer appropriate (e.g. by switching to a value-based concept of equality
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instead of the default identity based equality) can explicitly flag
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themselves as being unhashable by setting ``__hash__ = None`` in the class
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definition. Doing so means that not only will instances of the class raise an
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appropriate :exc:`TypeError` when a program attempts to retrieve their hash
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value, but they will also be correctly identified as unhashable when checking
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``isinstance(obj, collections.Hashable)`` (unlike classes which define their
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own :meth:`__hash__` to explicitly raise :exc:`TypeError`).
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If a class that overrrides :meth:`__eq__` needs to retain the implementation
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of :meth:`__hash__` from a parent class, the interpreter must be told this
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explicitly by setting ``__hash__ = <ParentClass>.__hash__``. Otherwise the
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inheritance of :meth:`__hash__` will be blocked, just as if :attr:`__hash__`
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had been explicitly set to :const:`None`.
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If a class that overrrides :meth:`__cmp__` or :meth:`__eq__` needs to
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retain the implementation of :meth:`__hash__` from a parent class,
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the interpreter must be told this explicitly by setting
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``__hash__ = <ParentClass>.__hash__``. Otherwise the inheritance of
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:meth:`__hash__` will be blocked, just as if :attr:`__hash__` had been
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explicitly set to :const:`None`.
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.. method:: object.__bool__(self)
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