[Zope] Newbie - passing a list to an External Method

[Passin, Tom]

[ Dylan Reinhardt]

> Look extra carefully at any and all assignments you make in=20
> the external
> method.  In particular, it's possible you may have committed a common
> error with lists, ex:
>=20
> a =3D [1,2.3]
> b =3D a
> b =3D None
> # now the value of a is None!
>=20

That is not right.  a retains its value as expected.  To prove it,
here's  a transcript from an IDLE session, with Py2.1.3 -

>>> a =3D [1,2,3]
>>> b=3Da
>>> print b
[1, 2, 3]
>>> b=3DNone
>>> print a
[1, 2, 3]
>>>=20

Even when you start with=20

a=3Db=3D[1,2,3]

a still remains when you set b to None.

You must be mixing this up with some other situation in which both and b
have a reference to the same list, and a changed value in one then shows
up in the other.  For example -

>>> a=3Db=3D[1,2,3]
>>> a.append(4)
>>> print b
[1, 2, 3, 4]

This is different from re-assigning the variable to reference something
else like None.

Cheers,

Tom P