day14- dichotomy, anonymous functions, built-in functions and process-oriented programming

dichotomy

Dichotomy Look for the large amount of data, but the data need to be in good order. The main idea is to find the set :( array interval Array [Low, High])
(. 1) determines the position of the intermediate section K
(2) to find the value of T and array [k] comparison. If equal, look for the successful return of this position; otherwise identify new lookup zones, continue binary search.
Area is determined as follows: array [k]> T consists of an ordered array of apparent array [k, k + 1, ......, high]> T; therefore new interval array [low, ......, k- 1];
If the array [k] <T consists of an ordered array of apparent array [k, k-1, ......, low] <T; therefore new interval array [k + 1, ......, high]

Application: Look for a number in an ordered list

def search(nums, target):
    mid_index = len(nums)//2
    mid_num = nums[mid_index]
    if not nums:
        print('not exists!')
    if mid_num == target:
        print('find it!')      
    elif mid_num < target:
        nums = nums[mid_index+1:]
        search(nums,target)
    else:
        nums = nums[:mid_index]
        search(nums, target)

nums = [-1,0,3,5,9,12]
target = 9
search(nums,target)

find it!

Anonymous function

Anonymous function is a function defined by the keyword lambda

# 语法
lambda 参数: 逻辑代码

# 如返回x,y的和
func = lambda x,y:x+y
res = func(1,2)
print(res)

3

Anonymous function becomes ineffective once, generally not used alone, and the maximum value max / min Min / sorted sorting / map mapping / filter filters used in conjunction

Such as: return to the dictionary tallest man wages

# max(iterable,key=func)    将func函数的返回值作为判断的依据，返回iterable中的最大值
saraly_dict = {
    'nick':30000,
    'egon':100000,
    'tank':2000,
    'alex':10212
}

res = max(saraly_dict, key=lambda name:saraly_dict[name])
print(res)

egon

Such as: people return to the dictionary lowest wages

# min(iterable,key=func)    将func函数的返回值作为判断的依据，返回iterable中的最小值
saraly_dict = {
    'nick':30000,
    'egon':100000,
    'tank':2000,
    'alex':10212
}

res = min(saraly_dict, key=lambda name:saraly_dict[name])
print(res)

tank

Such as: the dictionary sort by salary

# sorted(iterable,key=func)    将func函数的返回值作为判断的依据，对iterable进行从小到大排序
saraly_dict = {
    'nick':30000,
    'egon':100000,
    'tank':2000,
    'alex':10212
}

res = sorted(saraly_dict, key=lambda name:saraly_dict[name])
res1 = sorted(saraly_dict, key=lambda name:saraly_dict[name], reverse=True) # 加关键字reverse=True则从大到小排序
print(res)
print(res1)

['tank', 'alex', 'nick', 'egon']
['egon', 'nick', 'alex', 'tank']

Such as: the list of characters plus 'abc'

# map(func,iterable)    将iterable中的每个元素传入到func中执行
lis = ['a', 'b','123']
res = map(lambda x:x+'abc', lis)
print(list(res))

['aabc', 'babc', '123abc']

Such as: the list of elements to 'ed' end screened

# filter(func,iterable)    将iterable中的每个元素传入到func中进行筛选
lis = ['sorted', 'teach', 'jumped']
res = filter(lambda x: x.endswith('ed'), lis)
print(list(res))

['sorted', 'jumped']

Built-in functions

1.bytes () encoded characters, the encoded into the specified character unicode

print(bytes('中国',encoding='utf8'))

b'\xe4\xb8\xad\xe5\x9b\xbd'

Conversion between 2.chr () / ord () and the ASCII code

print(chr(97))    # chr将ASCII码转换成对应字符
print(ord('a'))    # ord将字符转换成对应的ASCII码

a
97

3.divmod (x, y) modulo rounding

print(divmod(10,3))

(3, 1)

4.enumerate () Gets the index and value

res = ['a', 'b','c']
for k,v in enumerate(res):
    print(k,v)           

0 a
1 b
2 c

5.eval () removed the quotation marks from outside the data, which is what marks the data type of data type returned

print(eval('[1,2,3]'))

[1, 2, 3]

6.hash () can not change the hash, the hash is not variable

print(hash('abc'))    # 若里面是可变数据类型，则会报错

1361908011752591342

Absolute value 7.abs

print(abs(-10))

10

8.all () is true if the full return True, otherwise False

print(all(['abc',1]))

True

9.any () as long as there is a true will is True, False otherwise

print(any([0,'ab']))

True

10.bin () / oct () / hex () converted to a binary / octal hexadecimal form /

print(bin(17))
print(oct(17))
print(hex(17))

0b10001
0o21
0x11

11.dir () lists all the functions

import time
print(dir(time))

['_STRUCT_TM_ITEMS', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'altzone', 'asctime', 'clock', 'ctime', 'daylight', 'get_clock_info', 'gmtime', 'localtime', 'mktime', 'monotonic', 'perf_counter', 'process_time', 'sleep', 'strftime', 'strptime', 'struct_time', 'time', 'timezone', 'tzname']

12.frozenset () set immutable

print(frozenset([1,3,2]))

frozenset({1, 2, 3})

13.globals () / locals () view the global variables / local variables

14.pow(x,y,z)

print(pow(3,2,4))    # 返回 x**y%z

1

15.round () rounding

print(round(3.4))

3

16.sum () sum

print(sum([1,2,3]))

6

17 .__ import __ () by introducing string module

m = __import__('time')
print(m.time())        # 就是导入了time模块，m.time()就是运行time.time()

1559730202.8626022

Process-oriented programming

According to a certain order, the order of each step can be viewed as functions, this input function is a function of the output, which is called process-oriented programming

advantage:

• Logical, straightforward
• Each function can be independently written

Disadvantages:

• There will be some link between each other, interrupted the previous step, the next step will break the
• There is a change in the function, other functions will be changed
• Poor scalability