diff options
Diffstat (limited to 'Misc')
| -rw-r--r-- | Misc/NEWS | 25 |
1 files changed, 16 insertions, 9 deletions
@@ -29,25 +29,32 @@ Core language, builtins, and interpreter 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 @@ Core language, builtins, and interpreter 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 |