Following functions kept:
```pycon
>>> import inspect
... with_args = []
... with_kwargs = []
... for n in dir(mpmath):
... m = getattr(mpmath, n)
... try:
... s = inspect.signature(m)
... except:
... continue
... if any(_.kind == inspect._ParameterKind.VAR_POSITIONAL for _ in s.parameters.values()):
... for name in s.parameters:
... if s.parameters[name].kind == inspect._ParameterKind.VAR_POSITIONAL and name == 'args':
... with_args.append(n)
... break
... if any(_.kind == inspect._ParameterKind.VAR_KEYWORD for _ in s.parameters.values()):
... with_kwargs.append(n)
... print(with_args)
... print(with_kwargs)
...
['arange', 'ellipe', 'ellippi', 'linspace', 'matrix', 'ones', 'timing', 'zeros']
['multiplicity', 'timing']
```
We need support for multiple signatures in the first case. In the
second - it's impossible to implement these functions without kwargs.
Closes#1056
We do not use subclassing in order to keep it as simple as possible. This
precludes the use of `@abstractmethod`, however it keeps the
`__init__`/`__new__` unchanged.
Not using subclassing/`@abstractmethod` means that checks whether the inferface
conforms to the requirements of the ABC are not done. Given the simplicity of
the interface in our case, this is the prefered approach. Conformity of the
interface is checked durring developpement.
Examples
========
`issubclass` works as well.
```
In [12]: import numbers
In [13]: import mpmath
In [14]: isinstance(mpmath.mpf(0.23), numbers.Complex)
Out[14]: True
In [15]: isinstance(mpmath.mpf(0.23), numbers.Real)
Out[15]: True
In [16]: isinstance(mpmath.mpf(0.23), numbers.Rational)
Out[16]: False
```
```
In [18]: isinstance(mpmath.mpc(0.23), numbers.Complex)
Out[18]: True
In [19]: isinstance(mpmath.mpc(0.23), numbers.Real)
Out[19]: False
```
```
In [20]: isinstance(mpmath.mpi(0.23), numbers.Complex)
Out[20]: True
In [21]: isinstance(mpmath.mpi(0.23), numbers.Real)
Out[21]: True
In [22]: isinstance(mpmath.mpi(0.23), numbers.Rational)
Out[22]: False
```
```
In [23]: isinstance(mpmath.mpi(0.23+1j), numbers.Complex)
Out[23]: True
In [24]: isinstance(mpmath.mpi(0.23+1j), numbers.Real)
Out[24]: False
```
Sergey B Kirpichev