Zero basic mastery of Python entry to actual combat

Python basics

Note: It is suitable for Mengxin to learn python and the content inside will be continuously updated!

About for loop

Example: Create a data set containing random integers from 1 to 10, totaling 100 numbers, and count the number of times each number appears.

// 方法1
import random //引入random模块
 lst = []    //定义一个空列表
d = dict() //定义一个空字典
for i in range(100): //循环100次
    n = random.randint(1,10) //每循环一次随机拿到1——10以内的任意一个数
    if n in d :
        d[n]+=1  //如果这个数作为键在字典里，值加1
    else:
        d[n]=1 //否则值等于1
print(d)

//方法2
import random 
lst=[]
for i in range(100):
    n=random.randint(1,10)
    lst.append(n)
d={
    
    }
for n in lst:
    if n in d:
         d[n]+=1
    else:
         d[n]=1

Functions commonly used in for loops

1. range()
2. zip()
3. enumerate( )
4. List comprehension

Example: Find a number within 100 that is divisible by three

lst=[]
for i in range(100):
    if i % 3 == 0;
    lst.append(i)
print(lst)

Use list analysis to find the number within 100 that is divisible by three

>>>[i for i in range(100) if i % 3 == 0]

结果是：[0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99]

>>>range(0, 100, 3)
>>>list(range(0, 100, 3))

Use the range method to add the corresponding values ​​of two lists

c=[1，2，3，4，5]
d=[6，7，8，9，1]
r=[]
for i in range(len(c))://把列表中的每一个元素所对应的索引拿出来了
     r.append(c[i]+d[i])

Use the zip method to add the corresponding values ​​of the two lists

 c=[1，2，3，4，5]
 d=[6，7，8，9，1]
r=[]
for x,y in zip(c,d):
     r.append(x+y)
print(r)

enumerate() method: enumerate returns index value

>>>s=['one','two','three']
>>>list(enumerate(s))
[(0, 'one'), (1, 'two'), (2, 'three')]//得到索引和值

Example: The string s='life is short You need python'. Count the number of occurrences of each letter in this string.

s='life is short You need python'
lst = []   //定义一个空列表
d = dict() //定义一个空字典
for i in s: //循环获取s中的每个字母
   if i.isalpha(): //判断循环得到的是否是一个字符，是字符则执行后面的代码块 否则返回false
       if i in d : 
           d[i]+=1  //'键'放在字典里并且'值'加1
       else:
           d[i]=1 
print(d)

About the while loop

格式： while[condition]：
statements

a=0
while a<3:
    s=input("input your lang:")
    if s=='python':
        print("your lang is {0}".format(s))
        break  //当代码执行到这里时，会跳出当前循环（此处跳出while 执行print("the end a:",a)）
    else:
        a+=1
        print("a=",a)
print("the end a:",a)

a=11
while a>0:
    a-=1;
    if a%2==0:
        continue
        print(a)
    else:
        print(a)

Use the while loop to make a small game:
make a guessing game that meets the following functions:
1. The computer randomly generates a positive integer within 100;
2. The user enters a number through the keyboard and guesses the random number generated by the computer.
Note: There is no limit to the number of user input.

import random
computer_name = random.randint(1,100) #表示从1——100以内随机取一个数
while True:   #表示一直循环，直到遇到结束标志
    user_name = input("请输入你要猜测的数字:")  #获得的是字符串类型
    if not user_name.isdigit():
        print("请输入1——100以内的整数" )
    elif int(user_name)<0 or int(user_name)>=100:
        print("请输入1——100以内的整数")
    else:
        if int(user_name)==computer_name:
            print("you are win")
            break
        elif int(user_name)<computer_name:
            print("you are smaller")
        else :
            print("you are bigger")
#注：并非是最优代码，但程序完全正确！因为此时作者也处在学习阶段！