Inplement __str__ for all Xform classes

[junchaoxia]

Currently the information on the individual pipeline items were printed out something as <aspire.source.xform.Downsample object at 0x2b112a581f98>. It will be more friendly if we implement __repr__ for all Xfrom classes to generate a short name such as Downsample.

[vineetbansal]

I'd recommend passing in an optional name in the base Xform constructor, which falls back to the class name on None.

In any case, __str__ is the one you want to override here, not __repr__. It's very rare to better the default __repr__ for any class (one usually wants the class name and the memory address for debugging purposes anyway).

[junchaoxia]

Got it. Changed the title.

[janden]

Agreed. In addition to the name, it might be good to include some of the important parameters (downsampling factor for Downsample, and so on).

[junchaoxia]

The issue has been fixed in PR #253. Closing now.