如何在不使用 replace() 方法的情况下从字符串中删除特定元素？

Question

I'm trying to traverse through a string using its indices and remove specific elements. Due to string length getting shorter as elements are removed, it always goes out of range by the time the final element is reached.

Here's some code to ilustrate what I'm trying to do. For example, going from "1.2.3.4" to "1234".

string = "1.2.3.4"
for i in range(len(string)):
    if string[i] == ".":
        string = string[:i] + string[i+1:]

I know there are alternate approaches like using string method called replace() and I can run string = string.replace(string[i], "", 1) OR I can traverse through individual elements (not indicies).

But how would I solve it using the approach above (traversing string indices)? What techniques can I use to halt the loop after it reaches the final element of the string? Without continuing to advance the index, which will go out of range as elements are removed earlier in the string.

Answer 1

Use this:

string = "1.2.3.4"
res = ""
for s in string: 
    if s != '.': 
        res += s

The result is of course '1234'.

Answer 2

it could be done like this (with a try/except block), but that's not really a great way to approach this problem (or any problem)

string = "1.2.3.4"


for i in range(len(string)):
    try:
        if string[i] == ".":
            string= string[:i]+string[i+1:]
    except:
        IndexError

result is 1234

The only real change of course is that by adding a try/except around our loop, we save ourselves from the IndexError that would normally come up once we try to access an element in the string that is now out of bounds

Once that happens, the Exception is caught and we simply exit the loop with our finished string

Answer 3

you can use the re module:

import re
string = "1.2.3.4"
string = re.sub('\.','',string)
print(string)

Answer 4

If I understand correctly, you want to modify a string by its index while the length of it keep changing.

That's pretty dangerous.

The problem you ran into is caused by range(len(string)) .See, once the range is fixed, it won't change.And in the loop, string changes, it gets shorter, and that's why you got out of range error.

So what you want to do is to track the string while looping, and use if-else to find the '.'s, here is an example:

string = '1.2.3.4'
i = 0
while i < len(string):
    if string[i] == '.':
        string = string[:i] + string[i+1:]
    else:
        i += 1

Still, there are plenty of ways to deal with your string, don't use this, this is not good.