python中的回文范围

Question

我学习Python已经15天了，下面代码的每一步都需要您的指导。 此代码检查由两个3位数字的乘积生成的最大回文

非常抱歉，我提出了一个最愚蠢的问题

largest_palindrome = 0
for x in range(999,100,-1):
    for y in range(x,100,-1):
        product = x*y
        check = str(x*y)
        if check ==  check[::-1]:
            if product > largest_palindrome:
                largest_palindrome = product
print(largest_palindrome) ```

 - Need clarification on the below:

for x in range(999,100,-1): #why is -1 introduced here. what is the range it is checking in (999,100,-1)
for y in range(x,100,-1): # why is x introduced in y loop. how much times it will check the range.
product = x*y
check = str(x*y)# why is string introduced here ?

if check ==  check[::-1]: # what does this line mean?
if product > largest_palindrome:
largest_palindrome = product

print(largest_palindrome)

Answer 1

对于范围内的x（999100，-1）：#为什么这里引入了-1。它正在签入的范围是多少（999100，-1）

Answer: x is iterating from 999 to 100, decreasing by 1 on each loop

对于范围（x，100，-1）内的y:#为什么在y循环中引入x。它将检查范围的多少次

Answer: y is iterating from x (from upper loop) until 100. This loop will be running for each value of x from upper loop

check=str（x*y）#为什么这里引入字符串

Answer: converting the product from int to str so that we can reverse the number. Below is possible for string not for int, so it is converted to string

如果check==check[：-1]：#这行是什么意思

Answer: check[::-1] is the reverse string of chech. We check here if reversed string and non-reversed string are same (pallindrome if same)