GeezerVison

As I already had implementation I though PR might be helpful for others to see and evaluate.

From all the different extensions of functools.partial I think this one is the best. It is relatively simple and exposes all missing functionality. Other partial extensions that I have seen lack functionality and would not provide complete argument ordering capabilities and/or are too complicated in relation to what they offer.

Implementation can be summarised as follows:
a) All trailing placeholders are removed. (Makes things simpler)
b) Throws exception if not all placeholders are filled on call
c) retains optimization benefits of application on other partial instances.

Performance penalty compared to current functools.partial is minimal for extension class. + 20-30 ns for initialisation and <4 ns when called with or without placeholders.

To put it simply, new functionality extends functools.partial so that it has flexibility of lambda / def approach (in terms of argument ordering), but call overhead is 2x smaller.

The way I see it is that this could only be justified if this extension provided completeness and no new functionality is going to be needed anywhere near in the future. I have thought about it and tried various alternatives and I think there is a good chance that this is the case. Personally, I don't think I would ever need anything more from partial class.

Current implementation functions reliably.

• Issue: functools.partial placeholders #119127