I frequently use this pattern to keep track of incoming data (for
example, to sum up sales of a specific brand):
=====================================
# read a brand record from a db
...
# keep track of brands seen
obj = brands_seen.get(brandname)
if obj is None:
obj = Brand()
brands_seen[brandname] = obj
obj.AddData(...) # this might for example keep track of sales
=====================================
as you might guess, brands_seen is a dictionary whose keys are
brandnames and whose values are brand objects.
Now the point is: is there a cleverer way to do this?
Basically what I'm doing is query the dictionary twice if the object
does not exist.
What I would like to understand is if there's some language built-in
logic to:
- supply a function which is meant to return a new object
- have the interpreter to locate the point in the dictionary where the
key is to be
- if the key is already there, it returns the value/object associated
and stops
- if the key is not there, it calls the supplied function, assigns the
returned value to the dictionary and return the object.
Giulio.
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