Python Second week study notes (1)

Depth copy

= = Compares the contents of the data, if it is true that the content is the same, the reference is different
= After the operation is executed, the reference address of the front and back two elements is the same

Shallow copy copy () List

Returns a new list
Reference types only copy reference addresses

Deep copy

Full copy. Include reference types

from copy import deepcopylst2=deepcopy.(lst)

Random number

import random

Randint (A, B)

Returns an integer between [a, b], closed interval

Choice (seq)

Randomly pick an element from an element of a non-empty sequence, such as

random.choice(range(10))

, randomly pick an integer from 0 to 9.

random.choice([1,3,5,7])

Randrange ([Start,] stop [, step])

Gets a random number in the collection that increments by the specified cardinality from within the specified range, the cardinality
The default value is 1.

Front closed rear Open

Random.shuffle (list)->none

Scrambled list elements in place

Sample (population, K)

Randomly remove k different elements from a sample space or a population (sequence or collection type), returning
A new list

Meta-group

Ordered set of elements

Initialization

t=tuple()t=()t=(1,)

Tuple queries are similar to lists

Tuple elements cannot be modified

Attention:
For tuples that contain complex objects, their reference addresses to complex objects cannot be changed, but the data contents of complex objects can be changed

Namedtuple

from collections import namedtuplePoint=namedtuple(‘Point‘,[‘x‘, ‘y‘])#Point=namedtuple(‘Point‘,‘x y‘) 第二种写法p1=Point(11，12)print(p1.x,p1.y)

Part of the source code:

if isinstance(field_names, str):    field_names = field_names.replace(‘,‘, ‘ ‘).split()field_names = list(map(str, field_names))typename = str(typename)

String Exercise Analysis: 1. Use the array to achieve the number of prime numbers within 100,000:

prime = [2]for i in range(3,100000,2):    flag = False    up = int(i**0.5)+1    for j in prime:        if i % j == 0:            flag = False            break        if j >= up:            flag = True            break        if flag:        prime.append(i)print(len(prime))

2. Yang Hui triangle: Method One (1) after iteration, add element 1:

n=6pre=[[1]]for i in range(n):    line=pre[i]    temp=[1]    for j in range(i):        temp.append(line[j]+line[j+1])    temp.append(1)    pre.append(temp)print(pre)

Method One (2):

n = 6pre = [1]for i in range(n):    temp = [1]    for j in range(i):        temp.append(pre[j] + pre[j + 1])    temp.append(1)    print(pre)    pre = temp

Method two list before or after complement element 0 iteration:

n=6pre=[1]for i in range(1,n):    pre.append(0)    newline=[]    for j in range(i+1):        var=pre[j-1]+pre[j]        newline.append(var)    print(newline)    pre=newline

Method Three (1) Create a well-width, full 1 list in advance, replace the calculated result with the number of corresponding positions in the list, and replace the symmetric two elements with a symmetric loop:

n=6triangle=[]for i in range(n):    temp=[1]*(i+1)    for j in range(1,i//2+1):        var=triangle[j-1]+triangle[j]        temp[j]=var        if i!=2*j:            temp[-j-1]=var    triangle=temp    print(temp)

Method Three (2):

n = 6triangle = []for i in range(n):    temp = [1] * (i + 1)    triangle.append(temp)    for j in range(1,i // 2 + 1):        var = triangle[i - 1][j - 1] + triangle[i - 1][j]        temp[j] = var        if i != 2 * j:            temp[- j - 1] = var    print(temp)    pre = temp

Method Four only opens up the maximum length of a list filled with 1, adding a temporary variable to store the replacement element, participate in the next calculation, take the symmetry, notice when changing the symmetric element, its index value to add an offset, the input when the list slices:

n = 6triangle = [1] * nfor i in range(n):    temp = 1    for j in range(1,i // 2 + 1):        var = temp + triangle[j]        temp = triangle[j]        triangle[j] = var        if i != j * 2:            triangle[- j - (n - i)] = var    print(triangle[: i + 1])

Bubble Method Sort

Time complexity O (n**2)

Method One:

lst=[9,8,7,6,5,4,3,2,1]cnt=0cnt_swap=0for i in range(len(lst)-1):    for j in range(len(lst)-i-1):        cnt+=1        if lst[j]>lst[j+1]:            lst[j],lst[j+1] = lst[j+1],lst[j]            cnt_swap+=1print(lst,cnt,cnt_swap)

Method Two (Optimization): Optimization point: If after the end of an inner loop, there is no element exchange operation, the remaining elements are already in order, no need to go down

#lst = [9,8,7,6,5,4,3,2,1]#lst = [1,2,3,4,6,5,7,8,9]lst = [2,1,3,4,5,6,7,8,9]cnt = 0cnt_swap = 0for i in range(len(lst) - 1):    flag = False     for j in range(len(lst) - i - 1):        cnt += 1        if lst[j] > lst[j + 1]:            lst[j],lst[j + 1] = lst[j + 1],lst[j]            flag = True            cnt_swap += 1    if not flag:        breakprint(lst,cnt,cnt_swap)

Python Second week study notes (1)