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Newsgroups: comp.lang.python
Date: Tue, 16 Oct 2012 21:16:01 -0700 (PDT)
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Subject: Re: overriding equals operation
From: 88888 Dihedral <dihedral88888@googlemail.com>
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Xref: csiph.com comp.lang.python:31459

Pradipto Banerjee=E6=96=BC 2012=E5=B9=B410=E6=9C=8816=E6=97=A5=E6=98=9F=E6=
=9C=9F=E4=BA=8CUTC+8=E4=B8=8B=E5=8D=889=E6=99=8259=E5=88=8605=E7=A7=92=E5=
=AF=AB=E9=81=93=EF=BC=9A
> I am trying to define class, where if I use a statement a =3D b, then ins=
tead of "a" pointing to the same instance as "b", it should point to a copy=
 of "b", but I can't get it right.
>=20
>=20
>=20
> Currently, I have the following:
>=20
>=20
>=20
> ----
>=20
>=20
>=20
> class myclass(object):
>=20
>         def __init__(self, name=3D'')
>=20
>                 self.name =3D name
>=20
>=20
>=20
>         def copy(self):
>=20
>                 newvar =3D myclass(self.name)
>=20
>                 return newvar
>=20
>=20
>=20
>         def __eq__(self, other):
>=20
>                 if instance(other, myclass):
>=20
>                         return self =3D=3D other.copy()
>=20
>                 return NotImplemented
>=20
> ----
>=20
>=20
>=20
> Now if I try:
>=20
>=20
>=20
> >>> a=3Dmyclass()
>=20
> >>> a.name =3D 'test'
>=20
> >>> b=3Da
>=20
What you really want is b=3Da.copy()=20
not b=3Da to disentangle two objects.

__eq__ is used in the comparison operation.=20
=20


> >>> b.name
>=20
> 'test'
>=20
> >>> b.name =3D 'test2'
>=20
> >>> a.name
>=20
> 'test2'
>=20
>=20
>=20
> I wanted b=3Da to make a new copy of "a", but then when I assigned b.name=
 =3D 'test2', even a.name became 'test2'.
>=20
>=20
>=20
> How can I rectify my code to make the __eq__() behave like copy()?
>=20
>=20
>=20
> Thanks
>=20
>=20
>=20
>=20
>=20
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d to be, nor should it be construed or used as, financial, legal, tax or in=
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>=20
>=20
>=20
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