DEPR: pct_change method/limit keyword

[jbrockmendel]

We should deprecate these and have users do obj.fillna(...).pct_change() instead.

[rhshadrach]

+1

[rhshadrach]

The default for method is pad. I would think we need to change the default to None before we can deprecate this outright.

[aalyousfi]

For 2.1.0, how to achieve the behavior of pct_change(fill_method=None) from the previous versions?

About this new change, the What's New page says to explicitly call ffill or bfill before calling pct_change. But my question is when I don't want to fill in any value (i.e. fill_method=None in previous versions).

@jbrockmendel @rhshadrach

[rhshadrach]

Thanks @aalyousfi; agreed we should allow the operation without warning. I propose we do not warn when fill_method=None is specified but otherwise continue with the deprecation. In 3.0, we will only allow None (raise on anything else) and then deprecate the fill_method keyword entirely, finally removing it in 4.0.

cc @jbrockmendel