Various behaviors of doctest

Steven D'Aprano steve+comp.lang.python at
Mon Feb 28 00:55:47 CET 2011

On Sun, 27 Feb 2011 08:55:10 -0800, Gnarlodious wrote:

> Using the doctest module, I get three different outputs:
> 1) From the Terminal shell, I see a full report: 
> python ~/Sites/Sectrum/ -v

Can we assume that, whatever that is, runs doctest.testmod()?

> 2) From the Terminal interactive session, I see an abbreviated report of
> only the failures:
> from doctest import testmod; testmod(Filter)

That's because you haven't specified the verbose option, either by 
injecting -v into sys.argv, or by verbose=True as an argument to testmod.

> 3) From a browser CGI, I see a named tuple: from doctest import testmod;
> doctest.testmod()
> This returns output like:
> TestResults(failed=1, attempted=5)
> The browser is invoking the exact same code as the shell doctest, so why
> should it return a named tuple? 

Because testmod *always* returns a named tuple. Read the Fine Manual at 
the interactive interpreter with:


> And how do I get it to return the full
> text so I can read it in the browser?

You don't. Consider a simplified version:

def testmod():
    print "lots of stuff"
    return (failures, total)

If you want to capture "lots of stuff", you have to either play nasty 
tricks with replacing standard out with a StringIO instance, or similar, 
or you have to look at the implementation of testmod() and re-implement 
it yourself.

Oh, here's a thought, if you're running Python 3, you could monkey-patch 


from stringio import StringIO
from functools import partial
buffer = StringIO()
myprint = partial(print, file=buffer)
doctest.print = myprint


Now somehow you have to pass buffer.as_string() to your CGI program, in 
whatever way you would normally do so.


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