Python 3 preparation: Py3 has no more the special object-function "__nonzero__"

[wluebbe]

The tool 2to3 renames __nonzero__ to __bool__. But the code has to depend on the Python version!

Note that this does not affect Cython extension types because Cython supports __nonzero__ and __bool__ independently of the Python version.

There are 25 affected modules.

This ticket is tracked as a dependency of meta-ticket ticket:16052.

[chapoton]

one step done (for the rings folder) in #21887

[chapoton]

another step in #21898

[chapoton]

Here is a brute-force tentative

• search and replace __nonzero__ by __bool__
• remove the former lines that have become __bool__ = __bool__

Let us see what happens..

---

New commits:

​5c0ed27	substitute __nonzero__ by __bool__
​fbf00d7	cleanup : removal of former alias for __nonzero__

[chapoton]

ok, this was too brutal.

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​d3182db

trac 16076 trying to get rid of the last nonzero

[chapoton]

ok, still not subtle enough..

[tscrim]

The way I've seen for this to be 2/3 compatible is to have __bool__ be an alias for __nonzero__ (or vice versa). The other way we could hack this is have in SageObject, as almost everything has this as a base class, we implement:

def __bool__(self):
    return self.__nonzero__()

[chapoton]

Hello Travis,

if you feel like giving it a try, please do. There is an abstract method __nonzero__ somewhere, which is the last place where __nonzero__ is not an alias (in python files).

[tscrim]

I think we should keep things as __nonzero__ for right now (up to having an explicit alias) for right now since we are in Python2 and to avoid the extra redirection. Although I guess to test how much this would cover things for Python3, it would have to be with a Python3 build.

[chapoton]

why sage-pending ?

[embray]

I might be misusing the milestone but this seems to be a very general task ticket not tied to a specific release milestone...?

[chapoton]

is this fixed by #24294?

[jdemeyer]

Replying to tscrim:

The way I've seen for this to be 2/3 compatible is to have __bool__ be an alias for __nonzero__ (or vice versa). The other way we could hack this is have in SageObject, as almost everything has this as a base class, we implement:

def __bool__(self):
    return self.__nonzero__()

I know that this reply is pointless is now, but I guess that something like that would have worked :-)

We are doing something similar for division in CategoryObject:

from __future__ import division

cdef class CategoryObject(SageObject):
    def __div__(self, other):
        return self / other

[embray]

Replying to chapoton:

is this fixed by #24294?

I don't think so by itself--I believe I've found some other examples affected by this (in non-Cython modules) but I could be mistaken.