When the "pydoc" module is imported, and the sys.stdout is overwriten, a end-of-line is sent to the console (on sdtout) when the help() function is sent.

to reproduce (this is on Python 2.5 but the same happens on Pythjon 3.1):

bash-3.2$ python2.5 -c "import pydoc; import sys; from StringIO import StringIO; sys.stdout = StringIO(); help(sys)"

bash-3.2$ 

(note the one empty line)

whereas:

bash-3.2$ python2.5 -c "import sys; from StringIO import StringIO; sys.stdout = StringIO(); help(sys)"
bash-3.2$ 

(no empty line)

The funny thing is that the difference only occurs if sys.stdout is redirected; if it is not, importing pydoc doesn't change anything to the output:

bash-3.2$ python2.5 -c "import pydoc; import sys; help(sys)" | wc
     256    1298   10690
bash-3.2$ python2.5 -c "import sys; help(sys)" | wc
     256    1298   10690
bash-3.2$ 




Note that this is related to 1700304, but is actually *one specific case* since *only one character* is not redirected - I would expect them all or none

Nice buglet, please take a look at Lib/pydoc.py to follow :)

As you point out, this is issue 1700304.
 
'plainpager', which outputs the help in these cases, uses 'sys.stdout.write(plain(text))', but Helper.help has a         "self.output.write('\n')" line that causes the behavior you see.

We could change "self.output.write('\n')" to "pager('\n')", but the real bug is that self.output is bound early to sys.stdout. So 'help()' is still redirecting to the old sys.stdout with your test.

I see a solution by turning Helper.output into a property, but it smells of over-engineering :) Passing all output to pagers should work too, unless we need Helper.output as a sort of sys.stderr.

The patch below shows that importing pydoc sets self.output prematurely and includes the "self.output.write('\n')" line.

Index: pydoc.py
===================================================================
--- pydoc.py    (revision 79447)
+++ pydoc.py    (working copy)
@@ -1765,6 +1765,7 @@
         elif isinstance(request, Helper): self()
         else: doc(request, 'Help on %s:')
         self.output.write('\n')
+        print >> sys.stderr, repr(self.output)

     def intro(self):
         self.output.write('''

Fixed in r83370 by making input and output properties -- as Daniel noted, that is a nice and backwards compatible solution.