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