F strings objects example (#30712)

* Upgraded node image to latest stable, v8.12 in docker compose

* f-strings example with capital letter F

* Example of using f-strings with an object

* Revert "f-strings example with capital letter F"

This reverts commit 8f498480ce.

* Revert "Upgraded node image to latest stable, v8.12 in docker compose"

This reverts commit e55dd116d2.

* feat: fixed header formatting

guide/english/python/python-f-strings/index.md

@@ -75,6 +75,7 @@ print(func)
 ```
 The sum of 3 + 5 is 8
 ```
+
 ### Joining the contents of a collection within a string:
 
 #### Input
@@ -90,9 +91,10 @@ print(list_str)
 ```
 List of fruits: Apple, Banana, Pear
 ```
+
 ### Convert an integer to 8-bit binary
 
-### Input
+#### Input
 
 ```python
 num = 42
@@ -100,10 +102,34 @@ num = 42
 print(f'The binary of {num} is {num:08b}')
 ```
 
-### Output
+#### Output
 ```
 The binary of 42 is 00101010
 ```
 
+### Using Object with f-strings
+
+#### Input
+
+```python
+class Book:
+    def __init__(self, title, author):
+        self.title = title
+        self.author = author
+
+    def __str__(self):
+        return f"{self.title} by {self.author}"
+
+
+book = Book("A Clash of Kings", "George R. R. Martin")
+
+print(f"{book}")
+```
+
+##### Output
+```
+A Clash of Kings by George R. R. Martin
+```
+
 ### Sources
 https://www.python.org/dev/peps/pep-0498/