Bn's constructor does not check its parameter is a number

[Sidnioulz]

Which results in Bn.__init__ serving arbitrary objects to abs(). According to the doc, the following types are acceptable:

"The argument may be a plain or long integer or a floating point number. If the argument is a complex number, its magnitude is returned."

You could either make Bn be an int or float, make its constructor explicitely reject wrong input types, or build a copy constructor (is that even a thing in Python!?).

[Sidnioulz]

https://gist.github.com/Sidnioulz/68df16e3c59ad0714614

[gdanezis]

Dealt with this in a pythonic way.