python function and error

通过函数调用函数，并传递参数

def binary_operation(func,op1,op2):
    return func(op1,op2)

def add(op1,op2):
    return op1+op2

def sub(op1,op2):
    return op1-op2

print(binary_operation(add,1,2))
print(binary_operation(sub,1,3))

# 产生函数的快捷凡是
def exp_factory(n):
    def exp(a):
        return a**n
    return exp
suqare=exp_factory(2)
type(suqare)
exp_factory(2)(3) #两个括号的函数调用

程序是一步一步设计的

函数嵌套

from time import clock # clock return CPU time or real time
def timer(f): # 传入一个函数
    def _f(*args):
        t0=clock()
        f(*args) # 任意参数
        return clock()-t0
    return _f
timer(binary_operation)(add,1,2)

指定输入参数的类型（防止输入量类型错误）

def greeting(name:str) ->str: # :str 参数的type -> str 返回值的type
    return 'Hello '+str(name) # 强制装换
greeting('zyj') 

lambda (anonymous function tiny function)

# Lambda function can have any number of arguments but only one expression. The expression is evaluated and returned. Lambda functions can be used wherever function objects are required
binary_operation(lambda op1,op2:op1*op2,2,4) # 定义parameter and return

# 函数作为列表元素
# [ ]用做index，因为()要声明函数，传入参数
many_fucntion=[
    (lambda x: x**2), # list 用“，”隔开
    (lambda x: x**3)]
print(many_fucntion[0](2),many_fucntion[1](2))

fliter function

# The filter() function in Python 
# takes in a function and a list as 
# arguments.

# The function is called with all the 
# items in the list and a new list 
# returned which contains items in 
# the list and a new list is returned 
# which contains items for which 
# the function evaluats to True.
my_list=[1,5,4,6,11,3,12]
new_list=list(filter((lambda x : x%2==0),my_list)) 

# Output :[4,6,12]
new_list
[i for i in my_list if i%2==0] # list comprehension

map (矩阵操作)

items=list(range(1,6))
squared=list(map((lambda x :x**2),items))
squared

def fahrenheit(T):
    return ((float(9)/5)*T+32)

def celsius(T):
    return (float(5)/9*(T-32))

temp=[36.5,37,37.5,39]
F=map(fahrenheit,temp)
list(F)

---
# 传入多个函数
def multiply(x):
    return (x*x)

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

func=[add, multiply]
for i in range(5):
    print(i)
    value=list(map((lambda x: x(i)),func))
    print(value)

reduce

# Reduce 遍历操作
from functools import reduce
reduce((lambda x,y:x+y),[47,11,42,13])

# 找出最小值
f=lambda a,b:a if (a>b) else b
reduce(f,[47,11,42,102,13])
# sum from 1 to 100
reduce((lambda x,y:x+y),range(1,101))

generators

%magic 调用magic function

%magic

之后的代码是之前基础的叠加。

exception——目的是，出现错误让程序继续运行。

a=0
try:
    1/0 # 产生异常，没有停止运行，而是做了什么。
# except:
except ZeroDivisionError :
    print("zeros") # 每个异常都有固定的名字
print("error")

程序员永远都是最懒的（防止盖起来复杂）

def extract_hero_img(current_page):
    start_link=page_hero.find('src="') #找到一个固定的特征，帮助确定位置
    start_quote=page_hero.find('"',start_link)
    end_quote=page_hero.find('"',start_quote+1)

    end_bracker=page_hero.find('>',end_quote)
    end_bracker
    start_bracker=page_hero.find('<',end_bracker+1)
    start_bracker
    print(page_hero[start_quote+1:end_quote])
    print(page_hero[end_bracker+1:start_bracker])
    return start_bracker
# 调用函数
entry_xuance=extract_hero_img(page_hero)
page_hero=page_hero[entry_xuance:]
extract_hero_img(page_hero)

使用循环注意：跳出的条件。

page_hero='''<ul class="herolist clearfix">
                            <li><a href="herodetail/506.shtml" target="_blank"><img
                                        src="//game.gtimg.cn/images/yxzj/img201606/heroimg/506/506.jpg" width="91"
                                        height="91" alt="云中君">云中君</a></li>
                            <li><a href="herodetail/505.shtml" target="_blank"><img
                                        src="//game.gtimg.cn/images/yxzj/img201606/heroimg/505/505.jpg" width="91"
                                        height="91" alt="瑶">瑶</a></li>
                                         src="//game.gtimg.cn/images/yxzj/img201606/heroimg/105/105.jpg" width="91"
                                        height="91" alt="廉颇">廉颇</a></li></ul>'''
start_index=0
last_index=0
def extract_hero_img(current_page):
    start_link=page_hero.find('src="') #找到一个固定的特征，帮助确定位置
    start_quote=page_hero.find('"',start_link)
    end_quote=page_hero.find('"',start_quote+1)

    end_bracker=page_hero.find('>',end_quote)
    start_bracker=page_hero.find('<',end_bracker+1)

    if current_page[start_quote+1:end_quote].startswith("//"):
        print(page_hero[start_quote+1:end_quote])
        print(page_hero[end_bracker+1:start_bracker])
        return start_bracker
    else :
        return -1
---
while True:
    page_hero=page_hero[last_index:]
    last_index=extract_hero_img(page_hero)
    if last_index==-1:
        break

小结：重复的东西函数化，多次用循环

quize code structure

# Define constant variables.
BATE=5.0
INITIAL_BALANCE=180000
addiation=24000

# Print the table of balance for each year.
banlance=INITIAL_BALANCE
bal_recores=[]

# your solution below
for i in range(1,21):
    total_each=(banlance+addiation)*(1+BATE/100)
    # print(total_each)
    bal_recores.append(total_each)
    interest=(banlance+addiation)*(BATE/100)
    banlance=total_each
#    print("{} {}".format(i,total_each))
#    print("year:{}. total:{}, interest:{}".format(i,total_each,interest)）
#    print("year:{},intest:{},balance:{}".format(i,interest,total_each))
    print("year:%4d, intest: %10.2f, balance:%10.2f" %(i,interest,total_each))

# plot figure
import matplotlib.pyplot as plt
fig, ax=plt.subplots()

ax.plot([i for i in range(1,20+1)],list(map((lambda x: x/1e4),bal_recores)))
ax.set(xlabel='n th year',ylabel='Money wan',title='How much I got')
ax.grid()

plt.show()