The error string contains the wrong function name erf. Maybe it makes sense to create a seperate function for this double extraction. The code is now copy pasted about 3 times. Please create a helper function which checks the amount of arguments and extracts the floating point number.

I completely agree with you that this copy-paste is horrible solution. I hoped to start a discussion from it.

I think this helper should be integrated into arg_check macro.

Whereve arguments are parsed and one of them is expected to be float it can actually be any other real number type macro should really check make_float, otherwise it'll be cpython incompatible

In [1]: class A:
   ...:     def __float__(self):
   ...:         return 1.0
   ...:     

In [2]: float(A())
Out[2]: 1.0

In [3]: import math

In [4]: math.log(A())
Out[4]: 0.0

So I hope you can give an advice on this one. what'd be the best way to aproach it?
Should it be just hardcoded into a macro as a special case?

I'm also pretty sure that the same implicit conversion should be done for for int

For example in this case I'm passing True as a port number for socket and it only fails, because of premissions, (it works from root!).

In [1]: import socket
In [3]: s = socket.socket()
In [4]: s.bind(('localhost', True))
---------------------------------------------------------------------------
PermissionError                           Traceback (most recent call last)
<ipython-input-4-ced4611914b1> in <module>()
----> 1 s.bind(('localhost', True))

PermissionError: [Errno 13] Permission denied

I would not yet place this automatic coercion in the arg_check macro yet. This macro is used really a lot. I suggest to create a helper function like coerce_into_float or something like that and place that in objfloat.rs for now. We can always extend the arg_check macro later when we require this logic in all places.

Basically my doubt is: Are you sure we always need to convert int to float at all function calls?

Ok, fair point.

One more question then, if you don't mind:

Can arg_check be used to check just a number of arguments, without checking a type?

It'll be handy to use arg_check to control a number of arguments a new helper function, to control their types.

Yes, this is possible. I believe you can set the type to None, and then it will extract the correct amount of arguments into the given rust names.

That's great. I'll try to come back with a fix as soon as possible