第九章、 类与面向对象
1) 类
基本类/超类/父类被导出类或子类继承。
Inheritance继承
Inheritance is based on attribute lookup in Python (in X.name expressions).
Polymorphism多态
In X.method, the meaning of method depends on the type (class) of X.
Encapsulation封装
Methods and operators implement behavior; data hiding is a convention by default.
class C1():
def __init__(self, who):
self.name = who
I1 = C1('bob')
print I1.name #bob
2) 命名空间
X = 11 # Global (module) name/attribute (X, or manynames.X)
def f():
print(X) # Access global X (11)
def g():
X = 22 # Local (function) variable (X, hides module X)
print(X)
class C:
X = 33 # Class attribute (C.X)
def m(self):
X = 44 # Local variable in method (X)
self.X = 55 # Instance attribute (instance.X)
print(X) # 11: module (manynames.X outside file)
f() # 11: global
g() # 22: local
print(X) # 11: module name unchanged
obj = C() # Make instance
print(obj.X) # 33: class name inherited by instance
obj.m() # Attach attribute name X to instance now
print(obj.X) # 55: instance
print(C.X) # 33: class (a.k.a. obj.X if no X in instance)
#print(C.m.X) # FAILS: only visible in method
#print(g.X) # FAILS: only visible in function
3) Self参数
指向对象本身
4) __init__构造器
如果没有__init__，则需要自己定义并赋值
class C1(): # Make and link class C1
def setname(self, who): # Assign name: C1.setname
self.name = who # Self is either I1 or I2
I1 = C1() # Make two instances,
#没有__init__，实例就是个空的命名空间
I1.setname('bob') # Sets I1.name to 'bob'
print(I1.name) # Prints 'bob'
构造器，创建时例时自动调用。
5) 继承搜索的方法
An inheritance search looks for an attribute first in the instance object, then in the class the instance was created from, then in all higher superclasses, progressing from the bottom to the top of the object tree, and from left to right (by default).
6) 一个例子
class AttrDisplay:
def gatherAttrs(self):
attrs = []
for key in sorted(self.__dict__):
attrs.append('%s=%s' % (key, getattr(self, key)))
return ', '.join(attrs)
def __str__(self):
return '[%s: %s]' % (self.__class__.__name__, self.gatherAttrs())
class Person(AttrDisplay): #Making Instances
def __init__(self, name, job=None, pay=0): # Add defaults
self.name = name # Constructor takes 3 arguments
self.job = job # Fill out fields when created
self.pay = pay # self is the new instance object
def lastName(self): # Assumes last is last
return self.name.split()[-1]
def giveRaise(self, percent): # Percent must be 0..1
self.pay = int(self.pay * (1 + percent))
class Manager(Person):
def __init__(self, name, pay):
Person.__init__(self, name, 'mgr', pay)
def giveRaise(self, percent, bonus=.10):
Person.giveRaise(self, percent + bonus)
if __name__ == '__main__': # Allow this file to be imported as well as run/tested
bob = Person('Bob Smith')
sue = Person('Sue Jones', job='dev', pay=100000)
print(bob)
print(sue)
print(bob.lastName(), sue.lastName())
sue.giveRaise(.10)
print(sue)
tom = Manager('Tom Jones', 50000)
tom.giveRaise(.10)
print(tom.lastName())
print(tom) 