need help in understanding python code line-CodePudding

Please help me in understanding the logic of the following function

def spy_game(nums):

    code = [0,0,7,'x']
    
    for num in nums:
        if num == code[0]:
            code.pop(0)   # code.remove(num) also works
       
    return len(code) == 1

CodePudding user response：

This code compare two lists "nums" and "code". if elements from both lists equal then it remove this element from list "code". and finally if length of list "code" equal 1 it should return True

Method "pop" remove the item at the given position in the list, and return it Method "remove" remove the first item from the list whose value is equal to x

CodePudding user response：

The function compares the object elements from nums (it seems to be an array) with the values in code, all in sequence.

Let's say that nums is [2,0,1,0].

The first iteration in the loop will find num to be 2, and that is compared with code[0] which is 0 so the comparison is false and continues with the following number.
The second iteration num will be 0, and that is compared with code[0] which is 0, so the comparison is true and pops the first element in code, the one we used to compare. Now code is [0,7,'x'] because the first element was removed.
Third iteration has num as 1 and the comparison with code[0] that again is 0 is false and continues with the next number.
Fourth iteration has num as 0 and it is compared with 0, so the comparison is true and again that first element of code is removed. Now code will be [7,'x'].

The result in this case is false because code ends with 2 elements instead of 1. The result will be true if the parameter nums includes in sequence the digits [0,0,7], no matter if they are mixed with other values. For example, this function will return true as well if you nums is [0,5,4,0,1,2,7] because the digits from code appears in the list.

The last 'x' is used in the function just to have some value in code to compare some element in nums after the last 7. For example, if there were no 'x' and nums is [0,0,7,1] the function will fail because once you try to compare the last element in nums you will have no more elements in code and code[0] will fail.