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Date: Sun, 25 Aug 2013 09:22:27 +0530
Subject: List getting extended when assigned to itself
From: Krishnan Shankar <i.am.songoku@gmail.com>
To: Python <python-list@python.org>
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Hi Python Friends,

I came across an example which is as below,

>>> var = [1, 12, 123, 1234]
>>> var
[1, 12, 123, 1234]
>>> var[:0]
[]
>>> var[:0] = var
>>> var
[1, 12, 123, 1234, 1, 12, 123, 1234]
>>>

Here in var[:0] = var we are assigning an entire list to the beginning of
itself. So shouldn't it be something like,

[[1, 12, 123, 1234], 1, 12, 123, 1234]

It happens when we do the below,

>>> var = [1, 12, 123, 1234]
>>> var[0] = var
>>> var
[[...], 12, 123, 1234]
>>>

Literally var[0] = var and var[:0] = var almost meens the same. But why is
the difference in output? Can anyone explain what happens when
slicing assignment and direct assignment.

Regards,
Krishnan

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<div dir=3D"ltr">Hi Python Friends,<div><br></div><div style>I came across =
an example which is as below,</div><div style><br></div><div style><div>&gt=
;&gt;&gt; var =3D [1, 12, 123, 1234]</div><div>&gt;&gt;&gt; var</div><div>[=
1, 12, 123, 1234]</div>
<div>&gt;&gt;&gt; var[:0]</div><div>[]</div><div>&gt;&gt;&gt; var[:0] =3D v=
ar</div><div>&gt;&gt;&gt; var</div><div>[1, 12, 123, 1234, 1, 12, 123, 1234=
]</div><div>&gt;&gt;&gt;=A0</div><div><br></div><div style>Here in var[:0] =
=3D var we are assigning an entire list to the beginning of itself. So=A0sh=
ouldn&#39;t=A0it be something like,</div>
<div style><br></div><div style>[[1, 12, 123, 1234], 1, 12, 123, 1234]</div=
><div style><br></div><div style><div style>It happens when we do the below=
,</div><div style><br></div><div>&gt;&gt;&gt; var =3D [1, 12, 123, 1234]</d=
iv>
<div>&gt;&gt;&gt; var[0] =3D var</div><div>&gt;&gt;&gt; var</div><div>[[...=
], 12, 123, 1234]</div><div>&gt;&gt;&gt;=A0</div><div><br></div></div><div =
style>Literally var[0] =3D var and var[:0] =3D var almost meens the same. B=
ut why is the difference in output? Can anyone explain what happens when sl=
icing=A0assignment=A0and direct assignment.</div>
<div style><br></div><div style>Regards,</div><div style>Krishnan</div></di=
v></div>

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