On 2:59 PM, 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.
The second argument to the fromkeys() method is an empty list object.
So that object is the value for *both* the new dictionary items. It
does not make a new object each time, it uses the same one.
You can check this for yourself, by doing
id(rg["a"]) and id(rg["b"])
I'd do something like :
rg = {}
for key in g.keys():
rg[key] = []
DaveA
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