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Q7_20.py
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140 lines (122 loc) · 3.64 KB
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# __call__
class Student(object):
def __init__(self, name):
self.name=name
def __call__(self):
print('anything')
s=Student('lyou')
s()
# Callable and callable(): whether object can be invoked.
callable(int)
#True
# __getattr__
# when invoking attribute that does not exist, the interpreter in PYTHON will try to invoke __getattr__(self, 'attr') to get attribute.
class Student(object):
def __init__(self):
self.name='Michael'
def __getattr__(self, attr):
if attr == 'score':
return 99
if attr == 'age':
return lambda:25 #return function
s=Student()
s.score
s.age()
# __iter__ ： always exist with __next__
# class can bu used for loop(for...in)
class Fib(object):
def __init__(self):
self.a, self.b = 0,1
def __iter__(self):
return self
def __next__(self):
self.a,self.b = self.b, self.a + self.b
if self.a > 1000:
raise StopIteration()
return self.a
for n in Fib():
print(n)
# __getitem__ : get the specified element. Fib()[5]
class Fib(object):
def __getitem__(self, n):
if isinstance(n, int):
a, b = 1, 1
for x in range(n):
a, b = b, a+b
return a
if isinstance(n, slice):
start = n.start
stop = n.stop
if start is None:
start = 0
a, b = 1, 1
L = []
for n in range(stop):
if n >= start:
L.append(a)
a, b = b, a + b
return L
f = Fib()
f[0:5]
f[:10]
# enum
from enum import Enum
Month = Enum('M',('Jan','Feb','Mar','Apr'))
for name, member in Month.__members__items():
print(name, member, member.value)
from enum import Enum, unique
@unique
class Weekday(Enum):
Sun = 0
Mon = 1
Tue = 2
day1 = Weekday.Mon
type(day1) # <enum 'Weekday'>
class Gender(Enum):
Male = 0
Female = 1
class Student(object):
def __init__(self, name, Gender):
self.name = name
self.gender = Gender
# custom Metaclasses
class Foo():
pass
f = Foo()
# the expression Foo() creates a new instance of class Foo.
# when the interpreter encounters Foo()
# the __call__() method of Foo's parent class is called
# the __call__() method in turn invokes the following
# __new__()
# __init__()
# if Foo does not define __new__() and __init__(), default methods are inherited from Foo's ancestry
# if Foo does define these methods, they override those from the ancestry, which allows for customized behavior when instantiating Foo
class ListMetaclass(type):
def __new__(cls, name, bases, attrs):
attrs['add'] = lambda self, value: self.append(value)
return type.__new__(cls, name, bases, attrs)
class MyList(list, metaclass=ListMetaclass):
pass
L=MyList()
L.add(1)
# cls: 当前准备创建的类的对象
# name: 类的名字
# bases: 类继承的父类的集合
# attrs: 类的方法集合
# ORM: object relational mapping 对象关系映射
class User(Model):
id = IntegerField('id')
name = StringField('username')
email = StringField('email')
password = StringField('password')
u.save()
class Field(object):
def __init__(self, name, column_type):
self.name = name
self.column_type = column_type
def __str__(self):
return '<%s:%s>' % (self.__class__.__name__, self.name)
class StringField(Field):
def __init__(self, name):
super(StringField, self).__init__(name, 'varchar(100)')