append to a sublist - please help

[Helmut Jarausch]

Hi,

I must be blind but I don't see what's going wrong
with

G=[[]]*2

G[0].append('A')
G[1].append('B')
print G[0]

gives

['A', 'B']

as well as
print G[1]

I was expecting
['A']
and
['B']
respectively.

Many thanks for enlightening me,
Helmut.

--
Helmut Jarausch

Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany

[Arnaud Delobelle]

Re: append to a sublist - please help

On Apr 6, 5:16 pm, Helmut Jarausch <jarau...@skyne t.bewrote:

Hi,
>
I must be blind but I don't see what's going wrong
with
>
G=[[]]*2
>
G[0].append('A')
G[1].append('B')
print G[0]
>
gives
>
['A', 'B']
>
as well as
print G[1]
>
I was expecting
['A']
and
['B']
respectively.
>
Many thanks for enlightening me,
Helmut.
>
--
Helmut Jarausch
>
Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany

This is in the top two FAQ, here is the relevant section:

http://www.python.org/doc/faq/programming/#how-do-i-create-a-multidimensional-list

HTH

--
Arnaud

[Lie]

Re: append to a sublist - please help

On Apr 6, 11:16 pm, Helmut Jarausch <jarau...@skyne t.bewrote:

Hi,
>
I must be blind but I don't see what's going wrong
with

The reason is:

G=[[]]*2

is doing a "shallow copy" of the blank list. The corrected code is
either:

G = [[] for _ in xrange(2)]

or

G = [[], []]

btw, this is a very frequently asked question