Ciccio wrote:
Hi all,
hope you can help me understanding why the following happens:
In [213]: g = {'a': ['a1','a2'], 'b':['b1','b2']}
In [214]: rg = dict.fromkeys(g.keys(),[])
In [215]: rg
Out[215]: {'a': [], 'b': []}
In [216]: rg['a'].append('x')
In [217]: rg
Out[217]: {'a': ['x'], 'b': ['x']}
What I meant was appending 'x' to the list pointed by the key 'a' in
the dictionary 'rg'. Why rg['b'] is written too?
Thanks.
rg = dict.fromkeys(g.keys(),[])
you are intialising the content with the same object [].
write instead
for key in g:
rg[key] = [] # python create a new list everytime it hits this line
For the same reason you never assign an empty list to default parameters
value:
In [37]: def a(p=[]):
....: return p
....:
In [38]: a1 = a()
In [39]: a2 = a()
In [40]: id(a1) ; id(a2)
Out[40]: 161119884
Out[40]: 161119884
Jean-Michel
--
http://mail.python.org/mailman/listinfo/python-list
