python判断质数prime number

1，输入一个数字，判断是否是一个质数

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代码自取

a = input('a number')  # data type:string
a = int(a)# change the string type to type integer
flag = 'is a prime number'  #
for x in range(2,a):
    if a%x==0: # judge if the variable a can divisible by x
        flag = 'is not a prime number'
        break  # end the current loop
if flag=="is a prime number":
    print(a,'is a prime number')
else:
    print(a,"is not a prime number")

 

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哥德巴赫猜想
#一个大于2的even number=prime number+prime number  

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  2，输出100到500之间所有质数

# question        
# output all prime number from 100 to 500.   

# way  
'''
step 1: output all  number from 100 to 500.  
step 2: judge if the variable a is a prime number       
step 3: if it is a prime number , output        
'''

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代码自取

# answer
for a in range(100,500):        
    flag = 'is a prime number'  #
    for x in range(2,a):
        if a%x==0: # judge if the variable a can divisible by x
            flag = 'is not a prime number' # change the flag
            break  # end the current loop
    if flag=="is a prime number":
        print(a,'is a prime number')
    #else:
        #print(a,"is not a prime number")

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# Homework        
# question 
1,print the largest prime number less than 100
2,output all prime number from 200 to 300
     

  练习英语和编程，有不对的表达，请大家帮忙指出来，谢谢！