06Python学习之路-抽象

06Python学习之路-抽象

斐波那契数列

fibs = [0, 1]
for i in range(10):
    fibs.append(fibs[-1] + fibs[-2])
    
输出
>>> fibs
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
>>> 

callable判断是否可以被调用

>>> import math
>>> x = 1
>>> y = math.sqrt
>>> callable(x)
False
>>> callable(y)
True

第一个函数

def hello(name):
    return "Hello, " + name + " !"
    
输出
>>> hello("YKDog")
'Hello, YKDog !'

利用函数打印斐波那契数

def fibs(num):

    fib = [0, 1];
    for i in range(num - 2):
        fib.append(fib[-1] + fib[-2])
    return fib
    
输出

>>> fibs(5)
[0, 1, 1, 2, 3]

字符串是值类型， 不是引用类型

def try_change(n):

    n = "YKDog"
    return

调用
>>> x = "YKPig"
>>> try_change(x)
>>> x
'YKPig'

列表是引用类型

def try_change(n):

    n[0] = "Good Game"
    return
    
调用
>>> x
['Good Game', 'haha']

引用 与 赋值

>>> x = ["Hello", "YKDog"]
>>> y = x[:]
>>> y == x
True
>>> y is x
False
>>> z = y
>>> z is y
True

初始化函数

def init(data):
    data["first"] = {}
    data["middle"] = {}
    data["last"] = {}
    
调用
>>> storage = {}
>>> init(storage)
>>> storage
{'first': {}, 'last': {}, 'middle': {}}

get使用

>>> dicta = {"a":"A", "b":"B"}
>>> dicta.get("a")
'A'

字符串的分割

>>> x = "**Hello**world*".split("*")
>>> x
['', '', 'Hello', '', 'world', '']
>>> x = " Hello ".split()
>>> x
['Hello']

函数的参数名和默认值 值得注意的是可以改变形参名字顺序 省略参数个数

def hello(name = "YKDog", greeting = "Hello"):

    #YKDog Hello, is default
    print("%s ,%s !" % (greeting, name))
    
调用   
    
>>> hello()
Hello ,YKDog !
>>> hello(name = "YTPig", greeting = "Hello")
Hello ,YTPig !
>>> hello(greeting = "Hello", name = "YTPig")
Hello ,YTPig !

>>> hello(name = "QF")
Hello ,QF !

>>> hello("hehe")
Hello ,hehe !

*元素收集 而不是 指针

def collection(x, y, z = 3, *pa, **pi):
    print(x, y, z)
    print(pa)
    print(pi)
    
调用
不能使用x = 1名字和形参一样 冲突 *是收集单个元素为元组， **是收集对应等式， 建立字典.

>>> collection(1, 2, 3, 4, 5, x = 1, y = 2)
Traceback (most recent call last):
  File "<pyshell#55>", line 1, in <module>
    collection(1, 2, 3, 4, 5, x = 1, y = 2)
TypeError: collection() got multiple values for argument 'x'
>>> collection(1, 2, 3, 4, 5, a = 1, b = 2)
1 2 3
(4, 5)
{'a': 1, 'b': 2}
>>> 

已经是元组 加 * 分散

def add(x, y): return x + y

>>> add(*(1, 2))
3

阶乘计算

def factorial(n):
    result = 1
    for i in range(1, n+1):
        result *= i
    return result 
    
结果
>>> factorial(5)
120