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]

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

 

[Lie]

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