Remove references to __cmp__.

This commit is contained in:
Georg Brandl 2008-09-24 09:11:47 +00:00
parent 23dbc6eeca
commit 05f5ab7ee3
5 changed files with 42 additions and 66 deletions

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@ -246,8 +246,8 @@ Glossary
hashable
An object is *hashable* if it has a hash value which never changes during
its lifetime (it needs a :meth:`__hash__` method), and can be compared to
other objects (it needs an :meth:`__eq__` or :meth:`__cmp__` method).
Hashable objects which compare equal must have the same hash value.
other objects (it needs an :meth:`__eq__` method). Hashable objects which
compare equal must have the same hash value.
Hashability makes an object usable as a dictionary key and a set member,
because these data structures use the hash value internally.

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@ -375,15 +375,14 @@ Decimal objects
.. method:: compare(other[, context])
Compare the values of two Decimal instances. This operation behaves in
the same way as the usual comparison method :meth:`__cmp__`, except that
:meth:`compare` returns a Decimal instance rather than an integer, and if
either operand is a NaN then the result is a NaN::
Compare the values of two Decimal instances. :meth:`compare` returns a
Decimal instance, and if either operand is a NaN then the result is a
NaN::
a or b is a NaN ==> Decimal('NaN')
a < b ==> Decimal('-1')
a == b ==> Decimal('0')
a > b ==> Decimal('1')
a or b is a NaN ==> Decimal('NaN')
a < b ==> Decimal('-1')
a == b ==> Decimal('0')
a > b ==> Decimal('1')
.. 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
be compared, or other cases where there is no defined ordering.
.. index::
single: __cmp__() (instance method)
single: __eq__() (instance method)
single: __ne__() (instance method)
single: __lt__() (instance method)
@ -181,15 +180,14 @@ be compared, or other cases where there is no defined ordering.
single: __gt__() (instance method)
single: __ge__() (instance method)
Instances of a class normally compare as non-equal unless the class defines the
:meth:`__eq__` or :meth:`__cmp__` method.
Non-identical instances of a class normally compare as non-equal unless the
class defines the :meth:`__eq__` method.
Instances of a class cannot be ordered with respect to other instances of the
same class, or other types of object, unless the class defines enough of the
methods :meth:`__cmp__`, :meth:`__lt__`, :meth:`__le__`, :meth:`__gt__`, and
:meth:`__ge__` (in general, either :meth:`__cmp__` or both :meth:`__lt__` and
:meth:`__eq__` are sufficient, if you want the conventional meanings of the
comparison operators).
methods :meth:`__lt__`, :meth:`__le__`, :meth:`__gt__`, and :meth:`__ge__` (in
general, :meth:`__lt__` and :meth:`__eq__` are sufficient, if you want the
conventional meanings of the comparison operators).
The behavior of the :keyword:`is` and :keyword:`is not` operators cannot be
customized; also they can be applied to any two objects and never raise an
@ -1642,8 +1640,7 @@ The constructors for both classes work the same:
The subset and equality comparisons do not generalize to a complete ordering
function. For example, any two disjoint sets are not equal and are not
subsets of each other, so *all* of the following return ``False``: ``a<b``,
``a==b``, or ``a>b``. Accordingly, sets do not implement the :meth:`__cmp__`
method.
``a==b``, or ``a>b``.
Since sets only define partial ordering (subset relationships), the output of
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:
Write the XML-RPC encoding of this :class:`DateTime` item to the *out* stream
object.
It also supports certain of Python's built-in operators through :meth:`__cmp__`
It also supports certain of Python's built-in operators through rich comparison
and :meth:`__repr__` methods.
A working example follows. The server code::
@ -273,8 +273,8 @@ internal use by the marshalling/unmarshalling code:
which was the de facto standard base64 specification when the
XML-RPC spec was written.
It also supports certain of Python's built-in operators through a
:meth:`__cmp__` method.
It also supports certain of Python's built-in operators through :meth:`__eq__`
and :meth:`__ne__` methods.
Example usage of the binary objects. We're going to transfer an image over
XMLRPC::

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@ -1168,8 +1168,7 @@ Basic customization
.. index::
single: comparisons
These are the so-called "rich comparison" methods, and are called for comparison
operators in preference to :meth:`__cmp__` below. The correspondence between
These are the so-called "rich comparison" methods. The correspondence between
operator symbols and method names is as follows: ``x<y`` calls ``x.__lt__(y)``,
``x<=y`` calls ``x.__le__(y)``, ``x==y`` calls ``x.__eq__(y)``, ``x!=y`` calls
``x.__ne__(y)``, ``x>y`` calls ``x.__gt__(y)``, and ``x>=y`` calls
@ -1198,28 +1197,11 @@ Basic customization
Arguments to rich comparison methods are never coerced.
.. method:: object.__cmp__(self, other)
.. index::
builtin: cmp
single: comparisons
Called by comparison operations if rich comparison (see above) is not
defined. Should return a negative integer if ``self < other``, zero if
``self == other``, a positive integer if ``self > other``. If no
:meth:`__cmp__`, :meth:`__eq__` or :meth:`__ne__` operation is defined, class
instances are compared by object identity ("address"). See also the
description of :meth:`__hash__` for some important notes on creating
:term:`hashable` objects which support custom comparison operations and are
usable as dictionary keys.
.. method:: object.__hash__(self)
.. index::
object: dictionary
builtin: hash
single: __cmp__() (object method)
Called for the key object for dictionary operations, and by the built-in
function :func:`hash`. Should return an integer usable as a hash value
@ -1228,37 +1210,35 @@ Basic customization
(e.g., using exclusive or) the hash values for the components of the object that
also play a part in comparison of objects.
If a class does not define a :meth:`__cmp__` or :meth:`__eq__` method it
should not define a :meth:`__hash__` operation either; if it defines
:meth:`__cmp__` or :meth:`__eq__` but not :meth:`__hash__`, its instances
will not be usable as dictionary keys. If a class defines mutable objects
and implements a :meth:`__cmp__` or :meth:`__eq__` method, it should not
implement :meth:`__hash__`, since the dictionary implementation requires that
a key's hash value is immutable (if the object's hash value changes, it will
be in the wrong hash bucket).
If a class does not define an :meth:`__eq__` method it should not define a
:meth:`__hash__` operation either; if it defines :meth:`__eq__` but not
:meth:`__hash__`, its instances will not be usable as dictionary keys. If a
class defines mutable objects and implements an :meth:`__eq__` method, it
should not implement :meth:`__hash__`, since the dictionary implementation
requires that a key's hash value is immutable (if the object's hash value
changes, it will be in the wrong hash bucket).
User-defined classes have :meth:`__cmp__` and :meth:`__hash__` methods
User-defined classes have :meth:`__eq__` and :meth:`__hash__` methods
by default; with them, all objects compare unequal (except with themselves)
and ``x.__hash__()`` returns ``id(x)``.
Classes which inherit a :meth:`__hash__` method from a parent class but
change the meaning of :meth:`__cmp__` or :meth:`__eq__` such that the hash
value returned is no longer appropriate (e.g. by switching to a value-based
concept of equality instead of the default identity based equality) can
explicitly flag themselves as being unhashable by setting
``__hash__ = None`` in the class definition. Doing so means that not only
will instances of the class raise an appropriate :exc:`TypeError` when
a program attempts to retrieve their hash value, but they will also be
correctly identified as unhashable when checking
``isinstance(obj, collections.Hashable)`` (unlike classes which define
their own :meth:`__hash__` to explicitly raise :exc:`TypeError`).
change the meaning of :meth:`__eq__` such that the hash value returned is no
longer appropriate (e.g. by switching to a value-based concept of equality
instead of the default identity based equality) can explicitly flag
themselves as being unhashable by setting ``__hash__ = None`` in the class
definition. Doing so means that not only will instances of the class raise an
appropriate :exc:`TypeError` when a program attempts to retrieve their hash
value, but they will also be correctly identified as unhashable when checking
``isinstance(obj, collections.Hashable)`` (unlike classes which define their
own :meth:`__hash__` to explicitly raise :exc:`TypeError`).
If a class that overrrides :meth:`__eq__` needs to retain the implementation
of :meth:`__hash__` from a parent class, the interpreter must be told this
explicitly by setting ``__hash__ = <ParentClass>.__hash__``. Otherwise the
inheritance of :meth:`__hash__` will be blocked, just as if :attr:`__hash__`
had been explicitly set to :const:`None`.
If a class that overrrides :meth:`__cmp__` or :meth:`__eq__` needs to
retain the implementation of :meth:`__hash__` from a parent class,
the interpreter must be told this explicitly by setting
``__hash__ = <ParentClass>.__hash__``. Otherwise the inheritance of
:meth:`__hash__` will be blocked, just as if :attr:`__hash__` had been
explicitly set to :const:`None`.
.. method:: object.__bool__(self)