How to capture the output of Python's help() function.

capture_help.py

import io
import sys


# Temporarily redirect stdout to a StringIO.
stdout = sys.stdout
s = io.StringIO()
sys.stdout = s
help(sys.intern)

# Don't forget to reset stdout!
sys.stdout = stdout

# Read the StringIO for the help message.
s.seek(0)
help_string = s.read()
print(help_string)

capture_help_correctly.py

import sys
import pydoc

# And of course there's what's probably the correct way to do it!
s = pydoc.getdoc(sys.intern)
print(s)

If your goal is to test behvior of help(whatever) (which can, for example, ensure some extension library you've written behaves as expected within the Python interpreter), something more along the lines of the first form, capture_help.py is best. That said, this example doesn't work on Python 3 due to new way of handling unicode strings. You will get exceptions similar to...

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Applications/VisIt.app/Contents/Resources/2.10.2/../bin/../2.10.2/darwin-x86_64/lib/python/lib/python2.7/site.py", line 455, in __call__
    return pydoc.help(*args, **kwds)
  File "/Applications/VisIt.app/Contents/Resources/2.10.2/darwin-x86_64/lib/python/lib/python2.7/pydoc.py", line 1794, in __call__
    self.help(request)
  File "/Applications/VisIt.app/Contents/Resources/2.10.2/darwin-x86_64/lib/python/lib/python2.7/pydoc.py", line 1842, in help
    self.output.write('\n')
TypeError: unicode argument expected, got 'str'

However, this ref does seem to work in both Python 2 and 3.