Python error: ValueError: substring not found

.py

So, I have this text that I must translated with library googletrans:

    <!-- ARTICOL START -->
    <p class="mb-40px">La muerte de Lorenzo el Magnífico puso fin al periodo.</p>
    <p class="mb-40px">My name is print</p>
    <p class="mb-40px">I must go home
    <p class="mb-40px">I love my laptop when is clean</p>
    <!-- ARTICOL FINAL -->

**The part of the python code with the problem is this:**

        for p in soup.findAll('p', class_='mb-40px'):
            begin_comment = str(soup).index('<!-- ARTICOL START -->')
            end_comment = str(soup).index('<!-- ARTICOL FINAL -->')
            if begin_comment < str(soup).index(str(p)) < end_comment:
                recursively_translate(p)

**It returns me the error:**

    Traceback (most recent call last):
      File "E:\BB\safary.py", line 143, in <module>
        begin_comment = str(soup).index('<!-- ARTICOL START -->')
    ValueError: substring not found
      
-----------ANSWERS----------

That error comes from the Beautifulsoup library, which controls the html tags in particular. 
In the example above, you are missing the closing tag `</p>` on line three.

Use this regex to find all unclosed html tags and close them with `</p>`

- <kbd>Ctrl</kbd>+<kbd>H</kbd>
- Find what: `^(<p class="mb-40px">)((?!</p>).)*$`
- Replace with: `$0</p>`
- **CHECK** *Wrap around*
- **CHECK** *Regular expression*
- **UNCHECK** `. matches newline`
- <kbd>Replace all</kbd>

Also, in Python code, is better to delete those 2 lines that contain ARTICOL START and ARTICOL FINAL, it is much simple this way

        for p in soup.findAll('p', class_='mb-40px'):
            if begin_comment < str(soup).index(str(p)) < end_comment:
                recursively_translate(p)