Python中用 def 关键字声明函数：

def sign(x):    if x>0:        return 'positive'    elif x<0:        return 'negative'    else:        return 'zero'for x in [-1,0,8]:    print(sign(x))   # print: negative,zero,positive

定义一个有默认值参数的函数：

def hello(name, loud=False):    if loud:        print('HELLO, %s!' % name.upper())    else:        print('Hello, %s' % name)hello('Bob') # Prints "Hello, Bob"hello('Fred', loud=True)  # Prints "HELLO, FRED!"