why __new__ ?

[sebhahn]

How comes that you use the __new__ method with self, even though it is a static method by definition?

https://github.com/jswhit/pyproj/blob/master/lib/pyproj/__init__.py#L608

[micahcochran]

Geod and Proj both have __new__ methods. Looking at the python docs, it looks like self should be changed to cls for the __new__ method. This is something I noted while looking at this and does nothing to answer your question, sebhahn.

[micahcochran]

I tried __init__ vs __new__ with the Geod class this a little when I was fixing issues #64 (PR #65). IMHO Cython's documentation isn't clear enough about what is happening during object creation regarding __new__ and __cinit__. So, some of this is my conjecture about how the functions __init__, __cinit__, and __new__.

For Proj, the __new__() is called first, which subsequently calls _proj.Proj.__new__(), which I assume is an alias for the __cinit__(). If you were to rename the Proj class function to __init__() it would happen after the function has been initialized. What is in __new__() is python code that parses parameters or makes ellipse calculations and passes it up to something that the __cinit__ which interfaces with the rest of the C code (proj.4 library).

That could probably be moved directly into the Cython __cinit__ functions, but then the code would also have to be compiled along with the rest of it.

The __new__ function has a cls parameter (which is currently confusingly called self as mentioned previously), which should not be stored to because the memory has not yet be allocated, which was what was happening in issue #64 .

TLDR The best answer is that __new__ was a design decision to add functionality in python code, then calls the corresponding Cython code to initialize the C library facing parts. __init__ would happen after __cinit__ meaning that the code in __new__ would not be able to feed into __cinit__.

[snowman2]

This has changed in the most recent version 2.1.0.