Lad wrote:
> I have a list
A dictionary.
> L={}
> Now I can assign the value
> L['a']=1
> and I have
> L={'a': 1}
>
> but I would like to have a dictionary like this
> L={'a': {'b':2}}
>
> so I would expect I can do
> L['a']['b']=2
>
> but it does not work. Why?
D["a"]["b"] = 2
translates to
D.__getitem__("a").__setitem__("b", 2)
When D doesn't already contain a key/value pair D = {"a": {}} the
__getitem__() call fails with a KeyError. If you don't know whether D
contains a key "a", use setdefault(key, value) which inserts the value only
if key is currently not in the dictionary. E. g.
>>> D = {}
>>> D.setdefault("a", {})["b"] = 42
>>> D.setdefault("a", {})["c"] = 24
>>> D
{'a': {'c': 24, 'b': 42}}
Peter
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