Both of the elif can simply be if. It's also more standard to write if not isinstance(number, int).

The elif isn't necessary in this case, it can just be if

FYI, the all() function returns True only if all the list elements evaluate to True.

However, you will also have to count there are four elements, so I like this solution. :)

If you want to catch anything and you don't care about what the actual exception was you can use:

except:

If you need to check a value is between two numbers you can reduce it to:

0 <= int(n) <= 255

The if statement is converting result to some boolean value. You can do the same thing without the if statement by simply casting:

return bool(result)

This solution is nice and simple but it would be better if the REGEX variable was named after what it was, rather than what it is. For example, naming it IP_REGEX would be more approproate reuasable solution. :)

This is just showing off. This is not clean, easily maintainbly code.

This is actually better than all of the other solutions because your code doesn't need to contain the definition of what an IP is at all.

I didn't like this one. It's confusing and very fiddly. There is no sense of achievement at the end.

This looks to be nice and clean because it is only two lines, but consider that putting 4 sepearte bits of information (the individual quanitities) onto separate lines. Spreading them over multiple lines may be longer but it is inherently clearer and better for version control when someone makes a change to a quantity.

This is a terribly verbose and confusing solution.