python 学习笔记(二)

python note 2

v0.1 2015.5.23 Sherlock init part4
v0.2 2015.5.31 Sherlock add part5

4. 函数

• 函数基础

#!/usr/bin/python

def test_add(a, b):
return a + b

print “1 + 2 =”, test_add(1, 2)

add_test = test_add
print “1 + 2 =”, add_test(1, 2)

# need “pass” to fill this “none content function”
def nop():
pass

# default input
def ball(r, color = “red”, vendor = “A”, llist = [1, 2, 3]):
llist.append(4)
print r
print color
print vendor
print llist

print “test_1”
ball(5)

print “test_2”
ball(5, “blue”)

print “test_3”
ball(5, vendor = “B”)

print “test_4”
ball(5, llist = [4, 5, 6])
ball(5)

# variable input
print
print “variable input test”
def sum(*number):
sum = 0
for i in number:
sum = sum + i
return sum
print “sum is”, sum(1, 2, 3)

num = [1, 2, 3, 4]
print “sum is”, sum(*num)

# key word input
print
print “key word input test”
def key_test(a, b, **c):
print a
print b
print c
print “key is”, key_test(1, 2)
print
print “key is”, key_test(1, 2, name = “Sherlock”)
print
dict_test = {“name” : “John”, “age” : 12}
print “key is”, key_test(1, 2, **dict_test)

1. 函数名是一个指向函数对象的引用，所以可以把一个函数名赋值给一个变量
2. 函数的参数可以是默认参数，可变参数，关键字参数等。
   当函数带默认参数时，默认参数需要是不可变参数。不然就像上面代码中显示的那样，
   如果函数中改变这个参数的值，以后这个参数的值相应的也都改变了。函数可以带可变
   参数, 可变参数可以直接传入函数，也可以先把所有参数组成一个列表，再通过*list
   传入。通过**dictionary的方式可以传入一个字典。

4. 面向对象

#!/usr/bin/python

class ball(object):
def init(self, r, color = “green”, vendor = “A”):
# init r, but we need not to declare r
self.r = r
self.color = color
# private element
self.__vendor = vendor

  def run(self):      print "ball is running"  def show_color(self):      print "color of ball is", self.color

# init an instance
ball_test_1 = ball(5)
ball_test_1.show_color()

print
ball_test_2 = ball(5, “red”)
ball_test_2.show_color()

print
ball_test_1.name = “John”
print ball_test_1.name

# test private element
# will appear error when run below command
#print ball_test_1.__vendor

# ok when run below command, but could not write this code, we should write a
# function to show ball’s vendor
print ball_test_1._ball__vendor

# inherit test
print
class football(ball):
def run(self):
print “football is running”

football_test_1 = football(10)
football_test_1.run()

# polymorphism test
print
def run(ball_t):
ball_t.run()
print “* *”
run(ball_test_1)
run(football_test_1)

print
print type(ball_test_1)
print type(football_test_1)

1. python中不需要在变量使用前先定义。
2. 私有变量需要加__的前缀

NOTE:
1. raw_input()输入的变量是字符串的，要输入数字需要：int(raw_input())