The ourput of pydoc.Helper help() method is always sent
to sys.stdout, even if Helper was supplied with
different input/output streams at initialization. Other
methods: listtopics etc. work as expected.

Example:
########################

import sys, pydoc
from StringIO import StringIO

buf=StringIO()
H=pydoc.Helper(sys.stdin,buf)

H.listtopics()
H.help("pydoc")
#at this point help on pydoc is printed to stdout
H.listtopics()

ss=buf.getvalue()
print ss
#at this point the list of topics is printed twice

########################

sys.version:
 '2.3 (#46, Aug 11 2003, 09:34:05) [MSC v.1200 32 bit
(Intel)]'

The problem persists in pydoc.py version 1.90 from CVS.

The reason for such behaviour is a call to global (in
module scope) function doc() at line 1628 in pydoc.py 1.90.
which doesn't care about Helper.input Helper.output
settings.

Confirmed. Is it relevant?

This patch redirects output from Helper.help to whatever output stream is passed to the Helper constructor. If no output stream is specified, the fault behavior is to pass the output to the OS pager.

Created a rietveld review
http://codereview.appspot.com/3202042

Thanks for the patch.  I commented there.

Patchset 3 on codereview looks good.  I’d like another review, so I’m adding the latest developers who touched pydoc.

Looks good; committed in r86957.

I just added another comment on Rietveld because I thought this was not fixed :)  Demo session:

  $ pydoc3.2 nonlocal  # will launch my pager, then print to stdout
  
  Related help topics: global, NAMESPACES

Kevin Le, would you like to write a failing test to confirm my bug?

confirmed, I'll take a closer look