the coercion code (in __mul__) should call __rmul__ when left or right is not coercible to a Sage element

[williamstein]

In this example the last print statement goes boom, but should work fine.

class Foo:
   def __rmul__(self, left):
      return 'hello'

H = Foo()
print int(3)*H
print 3*H

Component: coercion

Issue created by migration from https://trac.sagemath.org/ticket/2283

[jasongrout]

comment:1

Attachment: coercion-rmul.patch.gz

[jasongrout]

comment:2

Currently, (before this patch), if a class did

_r_action = __rmul__

things would work since the coercion model looks for an _r_action function as a last resort. This patch just makes this line unnecessary by having the coercion system also look for an __rmul__ function (which is standard python; see http://docs.python.org/ref/numeric-types.html)

Apparently this patch is controversial to at least one person, so it probably ought to be discussed.

[jasongrout]

comment:3

disclaimer: I don't know much at all about the coercion system; the above statements are from observations made in running examples.

[jasongrout]

comment:4

Attachment: coercion-rmul2.patch.gz

credit goes to gfurnish for noticing and helping track down the segfault that the original patch introduced!

Apply coercion-rmul2.patch instead of coercion-rmul.patch

[jasongrout]

comment:5

(and gfurnish also knew how to fix the error causing the segfault!)

[jasongrout]

comment:6

The patches above apply to 2.10.2.

[williamstein]

comment:7

Looks good to me. Thanks guys!

[sagetrac-mabshoff]

comment:8

Merged coercion-rmul2.patch in Sage 2.10.3.rc0