Codecov Report

Merging #496 into master will decrease coverage by 0.46%.
The diff coverage is 73.68%.

@@            Coverage Diff             @@
##           master     #496      +/-   ##
==========================================
- Coverage   76.41%   75.95%   -0.47%     
==========================================
  Files          64       64              
  Lines        5572     5572              
  Branches      895      894       -1     
==========================================
- Hits         4258     4232      -26     
- Misses       1020     1044      +24     
- Partials      294      296       +2

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Don't merge this yet, apparently the example given by @rickardraysearch is not tested. When running his test:

class X(System.Object):
    __namespace__ = "PyTest"

    def __init__(self, *args):
        print("Running X constructor, args = {0}".format(args))

x = X(1,2)

one can see that without the tp_call implementation given here, __init__ is always called without parameters. I'll add the test and try to make it work.

My very naive understanding of what is being done in pythonnet is as follows: Since there's no exact equivalence to a constructor in python indicating which base constructor to use (apart from calling one in __new__), pythonnet solves that by copying all base constructors to the subclass (AddConstructor in ClassDerivedObject.CreateDerivedType), but tries to run the python-defined __init__ with any remaining arguments from the constructor call (the eargs thingy in ConstructorBinder.InvokeRaw). That fails in this case, since InvokeRaw is called by the created CLR constructor, which has already lost the extra arguments.

Wouldn't it make more sense to have a ClassDerived.tp_init method that calls __init__ with whatever arguments are passed there? I have a commit at rickardraysearch/pythonnet@ a06fc32 that does more or less that with some bugs.

This is exactly what I was looking into right now :)