Python 学习 —— 进阶篇(装饰器、类的特殊方法)

　　Python基础部分学完之后，在进入其OOP部分前，先理解一下其装饰器这种结构，其功能可类比于Java中的面向切面编程，下面参见具体实例:

def log(f):
    def fn(x):
        print 'call ' + f.__name__ + '()...'
        return f(x)
    return fn

print '------------ 直接调  ----------- '
g = log(int)
g('')                      # 只调不打印返回值
print ''
print g('')                # 又调又打印输出结果

print '------------ 装饰器  ----------- '
@log
def myabs(x):
    if x < 0:
        return -x
    else:
        return x
print myabs(-17)

# 下面是错误的装饰器调用
# @log
# def add(x,y):
#     return x + y
# print add(4,8)

print '----------- 修改装饰器以支持多参数 -----------'
def log2(f):
    def fn(*args,**kv):
        print 'call ' + f.__name__ + '()...'
        return f(*args,**kv)
    return fn
@log2
def add(x,y):
    return x + y
print add(4,8)

print '-------------------- 带参的装饰器  ------------------------'
def log3(prefix):
    def log_decorator(f):
        def fn(*args,**kv):
            print '[%s] %s()...' % (prefix,f.__name__)
            return f(*args,**kv)
        return fn
    return log_decorator

print '---- 普通调用 -----'
def division(x,y):
    return x/y
log_decorator = log3('DEBUG')
division = log_decorator(division)
print division(18, 6)

print '---- 装饰器调用 ----'
@log3('DEBUG')
def multiplication(a,b):
    return a * b
print multiplication(3, 4)

　　下面针对Python类中几个常见的特殊方法重写:

class Student(object):
    def __init__(self,name,score):
        self.name = name
        self.score = score
    def __str__(self):
        return '(Student: %s, %s)' % (self.name,self.score)
    def __cmp__(self,s):
        if self.name < s.name:
            return -1
        elif self.name > s.name:
            return 1
        else:
            return 0
    def __call__(self,friend):
        print 'My name is %s...' % self.name
        print 'My friend is %s...' % friend.name

print '------- basic info output ------------'
John = Student('John',99)
Alice = Student('Alice',85)
print John
print Alice

print '\n------------ special called -------------'
John.gender = 'male'
print 'changed: ' , John # 没打印出来新属性gender，因为自定义的__str__方法中没有
print John.gender        # 确实给John添加了新属性
John(Alice)

print '\n------------ instance sort --------------'
L = [John,Alice]
print sorted(L)

print '\n------- print a sorted list -----------'
mylist = [Student('Alice',85),Student('Bob',90),Student('Tom',100)]
print sorted(mylist)