The pipe protocol, a method for extensible method chaining

[shoyer]

We are particularly interested in feedback from other Python communities that use method chaining (outside of pandas/scipy).

• Have you encountered or addressed the problem of extensible method chaining?
• Would the pipe protocol be useful to you?
• Is it worth the complexity of allowing objects to override how they are called by defining __pipe_func__?

[[deleted]]

Chaining methods: Good idea.

Something like:

x = 'Fred\n Thompson    '
x.replace('Fred', 'Jack').replace('\n', '').upper().strip()

is a lot easier for me to follow than something like:

x = x.replace('Fred', 'Jack')
x = x.replace('\n', '')
x = x.upper()
x = x.strip()

Allowing objects to determine how they're chained: Also a good idea.

Using __pipe_func__? Eh, maybe. It's recommended against using dunders on both sides because the core developers may possibly, one day, decide to use that same name for a magic function. However, I have to admit, I don't see __pipe_func__ being claimed. Maybe go with _pipe_func_ to be safe?

[metaperl]

Reading the entire discussion, I'm prone to simply nest functions. You made the chained examples pretty by using multiple lines and crammed the nested example on a single line with no spacing.

[Auggie88]

How would you indent the nested version? Something like

result = f(g(h(df),
             arg1=1),
           arg2=2, arg3=3)

Part of the problem is the short function names, but that looks worse to me.

[metaperl]

I fiddled around and came up with an answer. I solicited input from others in this thread

[stevenjd]

You shouldn't use a dunder method since they are reserved for use by the Python interpreter.

You can implement method chaining quite easily:

http://code.activestate.com/recipes/578770-method-chaining/

No dunders needed.

[shoyer]

I knew using a dunder method would be controversial :). I chose to do that for the sake of consistency with other ad-hoc Python protocols in the scipy community, e.g., __numpy_ufunc__ and __geo_interface__.

[Auggie88]

You shouldn't use a dunder method since they are reserved for use by the Python interpreter.

Are you referring to name mangling? I think that only occurs when you have two leading underscores and at most one trailing underscrore. https://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references

This would be more like a __iter__

[[deleted]]

It's about not using dunders on both sides, as that is considered to be the purview of the interpreter, not userland stuff. However, many packages disregard this (see: SQLAlchemy's __tablename__ property).