In Python, this is the best code I could come up with for
adding a new key, value to a dict
mytable.setdefault( k, [] ).append( v )
Naturally, right after writing my post I found that there is
an easier way:
table[ k ] = v
Just to be clear...these do two VERY different things:
>>> v1=42
>>> table1={}
>>> k='foo'
>>> table1.setdefault(k,[]).append(v1)
>>> table2={}
>>> table2[k]=v1
>>> table1, table2
({'foo': [42]}, {'foo': 42})
Note that the value in the first case is a *list* while the
value in the 2nd case, the value is a scalar. These differ in
the behavior (continuing from above):
>>> v2='Second value'
>>> table1.setdefault(k,[]).append(v2)
>>> table2[k]=v2
>>> table1, table2
({'foo': [42, 'Second value']}, {'foo': 'Second value'})
Note that table1 now has *two* values associated with 'foo',
while table2 only has the most recently assigned value.
Choose according to your use-case. For some of my ETL &
data-processing work, I often want the
mydict.setdefault(key, []).append(value)
version to accrue values associated with a given unique key.
-tkc
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