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Diffstat (limited to 'Misc/NEWS')
| -rw-r--r-- | Misc/NEWS | 43 |
1 files changed, 43 insertions, 0 deletions
@@ -3,6 +3,43 @@ What's New in Python 2.1 alpha 1? Core language, builtins, and interpreter +- The comparison operators support "rich comparison overloading" (PEP + 207). C extension types can provide a rich comparison function in + the new tp_richcompare slot in the type object. The cmp() function + and the C function PyObject_Compare() first try the new rich + comparison operators before trying the old 3-way comparison. There + is also a new C API PyObject_RichCompare() (which also falls back on + the old 3-way comparison, but does not constrain the outcome of the + rich comparison to a Boolean result). + + The rich comparison function takes two objects (at least one of + which is guaranteed to have the type that provided the function) and + an integer indicating the opcode, which can be Py_LT, Py_LE, Py_EQ, + Py_NE, Py_GT, Py_GE (for <, <=, ==, !=, >, >=), and returns a Python + object, which may be NotImplemented (in which case the tp_compare + slot function is used as a fallback, if defined). + + 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. + + 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 + 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. + - 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 @@ -70,6 +107,12 @@ Core language, builtins, and interpreter supported -- instead of calling __rcmp__, __cmp__ is called with reversed arguments. +- In connection with the coercion changes, a new built-in singleton + object, NotImplemented is defined. This can be returned for + operations that wish to indicate they are not implemented for a + particular combination of arguments. From C, this is + Py_NotImplemented. + - The interpreter accepts now bytecode files on the command line even if they do not have a .pyc or .pyo extension. On Linux, after executing |