- Add note about complex numbers.
- Changed description of rich comparisons to emphasize that < and >
(etc.) are each other's reflection. Also use this word in the note
about the demise of __rcmp__.
diff --git a/Misc/NEWS b/Misc/NEWS
index 27355ed..f4f0a5c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -29,25 +29,32 @@
Classes can overload individual comparison operators by defining one
or more of the methods__lt__, __le__, __eq__, __ne__, __gt__,
- __ge__. There are no explicit "reversed argument" versions of
- these; instead, __lt__ and __gt__ are each other's reverse, likewise
- for__le__ and __ge__; __eq__ and __ne__ are their own reverse
- (similar at the C level). No other implications are made; in
- particular, Python does not assume that == is the inverse of !=, or
- that < is the inverse of >=. This makes it possible to define types
- with partial orderings.
+ __ge__. There are no explicit "reflected argument" versions of
+ these; instead, __lt__ and __gt__ are each other's reflection,
+ likewise for__le__ and __ge__; __eq__ and __ne__ are their own
+ reflection (similar at the C level). No other implications are
+ made; in particular, Python does not assume that == is the Boolean
+ inverse of !=, or that < is the Boolean inverse of >=. This makes
+ it possible to define types with partial orderings.
Classes or types that want to implement (in)equality tests but not
the ordering operators (i.e. unordered types) should implement ==
and !=, and raise an error for the ordering operators.
- It is possible to define types whose comparison results are not
+ It is possible to define types whose rich comparison results are not
Boolean; e.g. a matrix type might want to return a matrix of bits
for A < B, giving elementwise comparisons. Such types should ensure
that any interpretation of their value in a Boolean context raises
an exception, e.g. by defining __nonzero__ (or the tp_nonzero slot
at the C level) to always raise an exception.
+- Complex numbers use rich comparisons to define == and != but raise
+ an exception for <, <=, > and >=. Unfortunately, this also means
+ that cmp() of two complex numbers raises an exception when the two
+ numbers differ. Since it is not mathematically meaningful to compare
+ complex numbers except for equality, I hope that this doesn't break
+ too much code.
+
- Functions and methods now support getting and setting arbitrarily
named attributes (PEP 232). Functions have a new __dict__
(a.k.a. func_dict) which hold the function attributes. Methods get
@@ -113,7 +120,7 @@
subtly. Since this was a terrible gray area of the language, this
is considered an improvement. Also note that __rcmp__ is no longer
supported -- instead of calling __rcmp__, __cmp__ is called with
- reversed arguments.
+ reflected arguments.
- In connection with the coercion changes, a new built-in singleton
object, NotImplemented is defined. This can be returned for