New features of classes ======================= A class can implement certain operations that are invoked by special syntax (such as subscription or arithmetic operations) by defining methods with special names. Special methods for any type ---------------------------- __repr__(self) --> string Used by the print statement and conversions (reverse quotes) to compute the string representation of an object. __cmp__(self, other) --> int Used by all comparison operations. Should return -1 if self<other, 0 if self==other, +1 if self>other. Due to limitations in the interpreter, exceptions raised by comparisons are ignored, and the objects will be considered equal in this case. Special methods for sequence and mapping types ---------------------------------------------- __len__(self) --> int Used by the built-in function len(). Should return the length of the object, which should be >= 0. Also, an object whose __len__() method returns 0 __getitem__(self, key) --> value Used to implement value = self[key]. Note that the special interpretation of negative keys (if the class wishes to emulate a sequence type) is up to the __getitem__ method. __setitem__(self, key, value) Used to implement self[key] = value. Same note as for __getitem__. __delitem__(self, key) Used to implement del self[key]. Same note as for __getitem__. Special methods for sequence types ---------------------------------- __getslice__(self, i, j) --> sequence Used to implement self[i:j]. Note that missing i or j are replaced by 0 or len(self), respectively, and len(self) has been added to negative i or j. __setslice__(self, i, j, sequence) Used to implement self[i:j] = value. Same note as for __getslice__. __delslice__(self, i, j) Used to implement del self[i:j]. Same note as for __getslice__. Special methods for numeric types --------------------------------- __add__, __sub__, __mul__, __div__, __mod__, __divmod__, __pow__, __lshift__, __rshift__, __and__, __xor__, __or__ Used to implement the binary arithmetic operations (divmod and pow are called by built-in functions). All have the call pattern func(self, other) --> number. __neg__, __pos__, __abs__, __invert__ Used to implement the unary arithmetic operations (-, +, abs and ~). All have the call pattern func(self) --> number. __nonzero__(self) --> int Used to implement boolean testing. An alternative name for this method is __len__. __coerce__(self, other) --> (self1, other1) or None Used to implement "mixed-mode" numeric arithmetic. Either return a tuple containing self and other converted to some common type, or None if no way of conversion is known. When the common type would be the type of other, it is sufficient to return None, since the interpreter will also ask the other object to attempt a coercion (but sometimes, if the implementation of the other type cannot be changed, it is useful to do the conversion to the other type here). __int__(self) --> int __long__(self) --> long __float__(self) --> float Used to implement the built-in functions int(), long() and float(). Notes ----- Except for __repr__ and __cmp__, when no appropriate method is defined, attempts to execute the operation raise an exception. For __repr__ and __cmp__, the traditional interpretations are used in this case.