how can I avoid abusing lists?

[Peter Otten]

Thomas Nelson wrote:

> I have this code:
> type1 = [0]
> type2 = [0]
> type3 = [0]
> map = {0:type1, 1:type1, 2:type3, 3:type1, 4:type2}  # the real map is
> longer than this
> 
> def increment(value):
> map[value][0] += 1
> 
> increment(1)
> increment(1)
> increment(0)
> increment(4)
> #increment will actually be called many times through other functions
> print type1[0], type2[0], type3[0]
> #should print "3 1 0"
> 
> This is exactly what I want to do: every time I encounter this kind of
> value in my code, increment the appropriate type by one.  Then I'd like
> to go back and find out how many of each type there were.  This way
> I've written seems simple enough and effective, but it's very ugly and
> I don't think it's the intended use of lists.  Does anyone know a
> cleaner way to have the same funtionality?

I don't think your code is ugly. Anyway, here are two more alternatives:

>>> types = [0] * 3
>>> dispatch = [0, 0, 2, 0, 1]
>>> for value in [1, 1, 0, 4]:
...     types[dispatch[value]] += 1
...
>>> types
[3, 1, 0]


>>> inflated = [0] * 5
>>> groups = [[0, 1, 3], [4], [2]]
>>> for value in [1, 1, 0, 4]:
...     inflated[value] += 1
...
>>> [sum(inflated[i] for i in group) for group in groups]
[3, 1, 0]

Peter