詳細內容看這裏A Guide to Python's Magic Methods
這裏也有1篇中文的翻譯部分https://pycoders-weekly-chinese.readthedocs.org/en/latest/issue6/a-guide-to-pythons-magic-methods.html
把python object提供的默認重載方法做了分類
1：構造和析構
__new__(cls, [...) 創造類
__init__(self,
[...)初始化
__del__(self)刪除類
演示代碼
from os.path import join
class FileObject:
'''Wrapper for file objects to make sure the file gets closed on deletion.'''
def __init__(self, filepath='~', filename='sample.txt'):
# open a file filename in filepath in read and write mode
self.file = open(join(filepath, filename), 'r+')
def __del__(self):
self.file.close()
del self.file2:自定義類的操作符比較運算
也就是 == >= 此類
__cmp__(self, other)比較
__eq__(self,
other)==
__ne__(self,
other)!=
__lt__(self,
other)<
__gt__(self,
other)>
__le__(self,
other)<=
__ge__(self,
other)>=
演示代碼
class Word(str):
'''Class for words, defining comparison based on word length.'''
def __new__(cls, word):
# Note that we have to use __new__. This is because str is an immutable
# type, so we have to initialize it early (at creation)
if ' ' in word:
print "Value contains spaces. Truncating to first space."
word = word[:word.index(' ')] # Word is now all chars before first space
return str.__new__(cls, word)
def __gt__(self, other):
return len(self) > len(other)
def __lt__(self, other):
return len(self) < len(other)
def __ge__(self, other):
return len(self) >= len(other)
def __le__(self, other):
return len(self) <= len(other)3:數值運算類
這裏不列舉
4:描述類
常見
__str__(self)
__repr__(self)
__unicode__(self)
5:屬性操作
__getattr__(self, name)
__setattr__(self,
name, value)
__delattr__
6:自定義序列操作
__len__(self)長度
__getitem__(self,
key)
__setitem__(self,
key, value)
__delitem__(self,
key)
__iter__(self)迭代器
__reversed__(self)反向
__contains__(self,
item)
__missing__(self,
key)子類繼承時候忽略
演示代碼
class FunctionalList:
'''A class wrapping a list with some extra functional magic, like head,
tail, init, last, drop, and take.'''
def __init__(self, values=None):
if values is None:
self.values = []
else:
self.values = values
def __len__(self):
return len(self.values)
def __getitem__(self, key):
# if key is of invalid type or value, the list values will raise the error
return self.values[key]
def __setitem__(self, key, value):
self.values[key] = value
def __delitem__(self, key):
del self.values[key]
def __iter__(self):
return iter(self.values)
def __reversed__(self):
return FunctionalList(reversed(self.values))
def append(self, value):
self.values.append(value)
def head(self):
# get the first element
return self.values[0]
def tail(self):
# get all elements after the first
return self.values[1:]
def init(self):
# get elements up to the last
return self.values[:-1]
def last(self):
# get last element
return self.values[-1]
def drop(self, n):
# get all elements except first n
return self.values[n:]
def take(self, n):
# get first n elements
return self.values[:n]7:反射
用來檢查類型
__instancecheck__(self,
instance)
__subclasscheck__(self, subclass)
8：函數化
__call__(self,
[args...])
9:上下文管理
__enter__(self)
__exit__(self,
exception_type, exception_value, traceback)
10：抽象類
http://docs.python.org/2/library/abc.html
11:綁定的描述符
__get__(self,
instance, owner)
__set__(self,
instance, value)
__delete__(self,
instance)
演示代碼
class Meter(object):
'''Descriptor for a meter.'''
def __init__(self, value=0.0):
self.value = float(value)
def __get__(self, instance, owner):
return self.value
def __set__(self, instance, value):
self.value = float(value)
class Foot(object):
'''Descriptor for a foot.'''
def __get__(self, instance, owner):
return instance.meter * 3.2808
def __set__(self, instance, value):
instance.meter = float(value) / 3.2808
class Distance(object):
'''Class to represent distance holding two descriptors for feet and
meters.'''
meter = Meter()
foot = Foot()
12：拷貝
__copy__(self)
__deepcopy__(self,
memodict={})深拷貝
13：存儲與提取
__getinitargs__(self)
__getnewargs__(self)
__getstate__(self)
__setstate__(self,
state)
__reduce__(self)
__reduce_ex__(self)
import time
class Slate:
'''Class to store a string and a changelog, and forget its value when
pickled.'''
def __init__(self, value):
self.value = value
self.last_change = time.asctime()
self.history = {}
def change(self, new_value):
# Change the value. Commit last value to history
self.history[self.last_change] = self.value
self.value = new_value
self.last_change = time.asctime()
def print_changes(self):
print 'Changelog for Slate object:'
for k, v in self.history.items():
print '%s\t %s' % (k, v)
def __getstate__(self):
# Deliberately do not return self.value or self.last_change.
# We want to have a "blank slate" when we unpickle.
return self.history
def __setstate__(self, state):
# Make self.history = state and last_change and value undefined
self.history = state
self.value, self.last_change = None, None