typo in Sequence

[dsm]

If you try to hash a mutable sequence, Sage complains that immutable sequences are unhashable..

sage: a = Sequence([1,2,3])
sage: hash(a)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)

/Applications/sage_devel/<ipython console> in <module>()

/Applications/sage/local/lib/python2.6/site-packages/sage/structure/sequence.pyc in __hash__(self)
    517         """
    518         if not self._is_immutable:
--> 519             raise ValueError, "immutable sequences are unhashable"
    520         if self.__hash is None:
    521             self.__hash = hash(tuple(self))

ValueError: immutable sequences are unhashable

which is backwards; immutable sequences are the only ones that are hashable.

[dsm]

Patch attached (mostly to see if I've got the mercurial-queue-to-patch process right.)

[dsm]

[Going with "misc" because I have no idea what to call this, and I'm tired of looking at "please change"..]

[aapitzsch]

Sorry, positive review was a bit too fast.

Could you change syntax of

raise ValueError, "mutable sequences are unhashable"

to

raise ValueError("mutable sequences are unhashable")

So we don't have to do it when porting sage to python3.

[aapitzsch]

dsm, please add your e-mail address to the patch file. ​http://www.sagemath.org/doc/developer/walk_through.html#submitting-a-change

[dsm]

Replying to aapitzsch:

raise ValueError("mutable sequences are unhashable")

So we don't have to do it when porting sage to python3.

Done, but since 2to3 handles this automatically, I'd've thought it made more sense to leave these alone until then.

I've also added an email address. I won't throw anyone under the bus, but I didn't conclude that names were mandatory while email addresses were merely preferred on my own. :-)

[aapitzsch]

Thanks

[jdemeyer]

This needs to be rebased to apply on top of #1819.

[dsm]

Lots of work to remove two characters from an error message! ;^) Rebased patch attached.