logic filters don't work with sp, spp, fp, or fpp about pyp3 HOT 1 OPEN

I think this is only a documentation bug if it's even a bug. It seems to be working as intended:

$ echo -e "1\n2" | pyp3 "'some' in sp" "This is some input" "ignore this line"
1

pyp IS filtering on sp, but it still only outputs p unless you tell it otherwise.

This could probably be made more clear in the documentation, esp w/re to the keep() and lose() functions.

So what if (ex for debugging) you want to read from a file or secondary without reading from stdin? It's a bit clunky, but:

$ pyp3 -t file -ib 2 "pp+fpp | 'some' in p"
This is some input

-b2 creates 2 blank lines as fake stdin.
-i filters out blank lines right away
pp+fpp combines the stdin and file contents. Since the input is blank_lines and we have --ignore_blanks, len(pp) == 0 and this just gives us fpp.
proceed with the second stage in the internal pip as if the inputs came from stdin.

You can do the same thing with "pp + spp" for secondary input.

from pyp3.