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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

One commit already so presumably not too much effort needed to close this one.

I just noticed the same bug described by Éric in msg127840. PR 8390 should fix it. Unfortunately, it wasn't easy to create a test case, so I skipped that part. I'm open to suggestions if you have an idea on how to write a simple test that reproduces the bug.
Éric, could you confirm that the attached PR fixes the bug?

Patch works!

New changeset d04f46c59f1d07d9bcc0ba910741296ac88d370d by Berker Peksag in branch 'master':
bpo-940286: Fix pydoc to show cross refs correctly (GH-8390)
https://github.com/python/cpython/commit/d04f46c59f1d07d9bcc0ba910741296ac88d370d

New changeset e9e6495eedd7fb588964ffa50e8bf2c5ce9c6051 by Miss Islington (bot) in branch '3.6':
bpo-940286: Fix pydoc to show cross refs correctly (GH-8390)
https://github.com/python/cpython/commit/e9e6495eedd7fb588964ffa50e8bf2c5ce9c6051

New changeset 14f58f0ff823ba71e3f21803c509d348626b6089 by Berker Peksag (Miss Islington (bot)) in branch '3.7':
bpo-940286: Fix pydoc to show cross refs correctly (GH-8390)
https://github.com/python/cpython/commit/14f58f0ff823ba71e3f21803c509d348626b6089