Float Conversion for #211

[makarchuk]

Implemented float conversion for functions in math module

[windelbouwman]

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.

[makarchuk]

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

[windelbouwman]

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?

[makarchuk]

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.

[windelbouwman]

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.

[makarchuk]

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

[windelbouwman]

Please create a helper function to extract the proper arguments as mentioned in another comment.

[makarchuk]

Sorry, I'm not sure it's ok here, but I have a habbit of force-pushing development branches occasionally, so I did this.

Anyway. It went ok without much code duplication without helper method, since I'm using (as you've adviced) arg_check to check number of arguments.

I've also added python based test for this.

[makarchuk]

I see that Travis build failed with

----------------------------- Captured stderr call -----------------------------
Traceback (most recent call last):
  File "/home/travis/build/RustPython/RustPython/tests/snippets/math.py", line 20, in <module>
    import math
  File "/home/travis/build/RustPython/RustPython/tests/snippets/math.py", line 21, in <module>
    assert(math.exp(2) == math.exp(2.0))
AttributeError: module 'math' has no attribute 'exp'

Which I don't really understand. It might be platform-dependent