Python基础篇(六)

retun空值，后面的语句将不再被执行

>>> def test():

...    print("just a test!")

...    return

...    print("will not be print")

...

>>> test()

just a test!

和Java类似，在传递参数时，当参数是字符串，元组时，传递的其实是拷贝，修改实际参数不会影响到形式参数。当参数是对象时，修改实际参数将会影响到形式参数。

>>> def changeName(name):

...    name = "Changed Name"

...    return name

...

>>> name = "Jhon Brown"

>>> changeName(name)

'Changed Name'

>>> name

'Jhon Brown'

实参为对象时的情况：

>>> def changeList(list):

...    list[0] = "Change Element"

...    return list

...

>>> list = ["one","two"]

>>> changeList(list)

['Change Element', 'two']

>>> list

['Change Element', 'two']

可以为实参取别名，这样当参数为多个的时候不会因位置错误而导致错误的结果

>>> def hello1(arg1,arg2):

...   print("%s %s" % (arg1,arg2))

...

>>> hello1(arg1 = "hello",arg2 = "world")

hello world

使用*收集剩余的参数：

>>> def printParams(title,*params):

...   print(title)

...   print(params)

...

>>> printParams("Params",2,3,4)

Params

(2, 3, 4)

定义和调用函数时都是用**，适用于元组或者字典。

>>> def with_stars(**database):

...    print(database["name"]+ "\'s age is" + database["age"])

...

>>> database = {"name":"Grubby","age":"29"}

>>> with_stars(**database)

Grubby's age is29

>>> def without_stars(database):

...    print(database["name"]+ "\'s age is" + database["age"])

...

>>> data = {"name":"Grubby","age":"29"}

>>> without_stars(data)

Grubby's age is29

>>> def story(kwd):

...     print("Once there is a %(player)s called %(name)s," % kwd)

...

>>> kwd = {"player":"king","name":"Chrile"}

>>> story(kwd)

Once there is a king called Chrile,

vars函数会返回一个字典，包含变量与赋值的关系

>>> x,y,z =1,2,3

>>> scope =vars()

>>> scope["x"]

1

递归调用的例子

def search(sequence,number,low=0,upper = None):

if upper is None :

upper = len(sequence) -1

if low == upper:

if sequence[low] == number:

return low

else:

return -1

else:

index = (int)((low + upper)/2)

if sequence[index] > number:

return search(sequence,number,low,index-1)  #这里的return是必须的，否则将没有返回值

elif sequence[index]

return search(sequence,number,index+1,upper)

else:

return index

sequence = [1,3,9,11,56]

search(sequence,3)

创建自己的类：

>>> class Person:

...    def setName(self,name):

...        self.name = name

...    def getName(self):

...        return self.name

...    def greet(self):

...        print("name is %s" % self.name)

...

>>> foo = Person()

>>> bar = Person()

>>> foo.setName("Luke")

>>> foo.getName()

'Luke'

>>> foo.greet()

name is Luke

>>> bar.setName("Sky")

>>> bar.getName()

Sky'

>>> bar.greet()

name is Sky

>>> bar.name

'Sky'

>>> bar.name = "Jason"     #属性使用类加上.直接使用

>>> bar.greet()

name is Jason

>>> class Bird:

...    __song = "spark"

...    def sing(self):

...       print(self.song)

...

>>> bird = Bird()

>>> bird.sing()

Traceback (most recent call last):

File "", line 1, in

File "", line 4, in sing

AttributeError: 'Bird' object has no attribute 'song'

>>> class Bird:

...    song = "spark"

...    def sing(self):

...       print(self.song)

...

>>> bird = Bird()

>>> bird.sing()

spark