初始循环的子字符串为空字符串，每次循环运行时，新字符串添加到子字符串或再次变为空字符串？

Question

def merge_the_tools(string, k):
strings_list = []                     
for i in range(0,len(string),k):               # incrementing the loop by k
    sub = (string[i:i+k])
    substring=''                           # empty substrings
    for x in sub:
        if x not in substring:          # removing the duplicates
            substring = substring + x
    strings_list.append(substring)            # adding it into empty list
print(*strings_list, sep='\n')      # printing the list

//此代码根据变量 'k' 将字符串分成子字符串，然后按顺序检查并从子字符串中删除重复项并打印新的子字符串。

输入：merge_the_tools('AABCAAADA', 3) 输出：AB CA AD

Answer 1

如果我没有正确理解您的问题，那么您是在询问是否对于外部 for 循环中的每次迭代，子字符串变量在为其分配变量之前是否为空字符串。每次启动循环时（即在部分字符串分配给 sub 之后），您都会将空字符串分配给变量 substring。

我将尝试使用 string = 'AABCAAADA', k = 3 逐步完成您的函数（我根据示例的需要多次复制了代码，并在代码中添加了注释）：

merge_the_tools('AABCAAADA', 3) #function call will trigger execution of function
strings_list = []                     
for i in range(0,len('AABCAAADA'), 3): #outer loop
# iteration 1: i = 0:
    sub = (string[0:3]) # = 'AAB'
    substring=''
    for x in sub: #inner loop
        # iteration 1.1: x = 'A'
        if 'A' not in substring: #substring is empty
            substring = '' + 'A' # substring = 'A' then go to next x in inner loop
        # iteration 1.2: x = 'A'
        if 'A' not in substring: #substring = 'A' -> condition not fullfilled, go to next x in inner loop
        # iteration 1.3: x = 'B'
        if 'B' not in substring: #substring = 'A'
        substring = 'A' + 'B' # substring = 'AB' -> last x in inner loop -> continue outer loop
    strings_list.append('AB') # strings_list = ['AB'], end of outer loop -> continue with next i of outer loop
# iteration 2: i = 3:
    sub = (string[3:6]) # = 'CAA'
    substring='' #here the empty string is reassigned to substring! 
    for x in sub: #inner loop
        # iteration 2.1: x = 'C'
        if 'C' not in substring: #substring is empty
            substring = '' + 'C' # substring = 'C' then go to next x in inner loop
        # iteration 2.2: x = 'A'
        if 'A' not in substring: #substring = 'C'
        substring = 'C' + 'A' # substring = 'CA' -> go to next x in inner loop
        # iteration 2.3: x = 'A'
        if 'A' not in substring: #substring = 'CA' -> condition not fullfilled, last x in inner loop -> continue outer loop
    strings_list.append('CA') # strings_list = ['AB', 'CA'], end of outer loop -> continue with next i of outer loop
# iteration 3: i = 6:
    sub = (string[6:9]) # = 'ADA'
    substring='' #here the empty string is reassigned to substring! 
    for x in sub: #inner loop
        # iteration 3.1: x = 'A'
        if 'A' not in substring: #substring is empty
            substring = '' + 'A' # substring = 'A' then go to next x in inner loop
        # iteration 3.2: x = 'D'
        if 'D' not in substring: #substring = 'A'
        substring = 'A' + 'D' # substring = 'AD' -> go to next x in inner loop
        # iteration 3.3: x = 'A'
        if 'A' not in substring: #substring = 'AD' -> condition not fullfilled, last x in inner loop -> continue outer loop
    strings_list.append('AD') # strings_list = ['AB', 'CA', 'AD'], end of outer loop -> last i of outer loop -> exit loop

print(*strings_list, sep='\n') #output :AB CA AD

希望这能让事情更清楚一些。另外，如果您不熟悉循环的概念，那里有很多很好的教程（只是 google）。

初始循环的子字符串为空字符串，每次循环运行时，新字符串添加到子字符串或再次变为空字符串？

the substring is empty string for initial loop , when everytime the loop runs , new string adds to the substring or it becomes empty string again?

python

python-3.x

string

jupyter-notebook

substr