Issue 1194449: pydoc requires o.nonzero() == True (original) (raw)

On Tue, 2005-05-03 at 07:44, Nadav Horesh wrote:

import numarray as N

a = N.array((2.3, 4.3)) N.version '1.3.1' help(a.stddev)

Traceback (most recent call last): File "<pyshell#11>", line 1, in -toplevel- help(a.stddev) File "/usr/local/lib/python2.4/site.py", line 328, in call return pydoc.help(*args, **kwds) File "/usr/local/lib/python2.4/pydoc.py", line 1647, in call self.help(request) File "/usr/local/lib/python2.4/pydoc.py", line 1691, in help else: doc(request, 'Help on %s:') File "/usr/local/lib/python2.4/pydoc.py", line 1475, in doc pager(title % desc + '\n\n' + text.document(object, name)) File "/usr/local/lib/python2.4/pydoc.py", line 297, in document if inspect.isroutine(object): return self.docroutine(*args) File "/usr/local/lib/python2.4/pydoc.py", line 1226, in docroutine if object.im_self: File "/usr/local/lib/python2.4/site-packages/numarray/generic.py", line 537, in nonzero raise RuntimeError("An array doesn't make sense as a truth value. Use any(a) or all(a).") RuntimeError: An array doesn't make sense as a truth value. Use any(a) or all(a).

help(a.sum)

In my opinion, this is a limitation (bug is maybe too strong) of pydoc, in that pydoc's docroutine method requires that an object be evaluable as a truth value and that the result be True. I think that's a common, but wrong, idiom.

I believe it's widely recognized that array's don't make much sense as truth values because it leads to code like this:

a = array(5); b = array(8) a & b array(0) if a & b: ... print "foo!" foo!

Numeric expressions like the above implicitly mean any(a & b) and appear to work but really contain subtle bugs.

Hence, in numarray and Numeric3 (now or eventually), the exception:

if a & b: ... print "foo!" ... Traceback (most recent call last): ... RuntimeError: An array doesn't make sense as a truth value. Use any(a) or all(a).

I think the pydoc docroutine() code should be changed to read:

if object.im_self is not None:

and that particular limitation will be removed. I submitted a patch.

Regards, Todd