I have a bunch of python classes that are responsible for validating files like so:

java file validator
html file validator
css file validator
javascript file validator

All of these classes define a validate_file(path) and validate_string(string) function.
In the client code of my application, I store all of these validators in an array and I iterate through all of them and call the methods on them in exactly the same way.
Is there a purpose in my case of defining a base "validator" class which defines these methods as abstract? How can I benefit from making these individual classes adhere to the base class? Or maybe in other words, what features would be unlocked if I had a base class with all of these validators implementing it?
If you ever write code that needs to process mixed types, some of which might define the API method, but which shouldn't be considered "validators", having a common base class for "true" validators might be helpful for checking types ahead of time and only processing the "true" validators, not just "things that look like validators". That said, the more complex the method name, the less likely you are to end up with this sort of confusion; the odds of a different type implementing a really niche method name by coincidence are pretty small.
That said, that's a really niche use case. Often, as you can see, Python's duck-typing behavior is good enough on its own; if there is no common functionality between the different types, the only meaningful advantages to having the abstract base class are for the developer, not the program itself:

Having a common point of reference for the API consumer makes it clear what methods they can expect to have access too
For actual ABCs with @abstractmethod decorated methods, it provides a definition-time check for subclasses, making it impossible for maintainers to omit a method by accident
What is the purpose of base classes in Python if you're already referring to the implementation classes consistently