I am trying to find a way to use a list of indexes to set values at multiple places in a list (as is possible with numpy arrays).
I found that I can map __getitem__ and a list of indexes to return the values at those indexes:
# something like
a_list = ['a', 'b', 'c']
idxs = [0, 1]
get_map = map(a_list.__getitem__, idxs)
print(list(get_map)) # yields ['a', 'b']
However, when applying this same line of thought to __setitem__, the setting fails. This probably has something to do with pass-by-reference vs pass-by-value, which I have never fully understood no matter how many times I've read about it.
Is there a way to do this?
b_list = ['a', 'b', 'c']
idxs = [0, 1]
put_map = map(b_list.__setitem__, idx, ['YAY', 'YAY'])
print(b_list) # yields ['YAY', 'YAY', 'c']
For my use case, I only want to set one value at multiple locations. Not multiple values at multiple locations.
EDIT: I know how to use list comprehension. I am trying to mimic numpy's capability to accept a list of indexes for both getting and setting items in an array, except for lists.
The difference between the get and set case is that in the get case you are interested in the result of map itself, but in the set case you want a side effect. Thus, you never consume the map generator and the instructions are never actually executed. Once you do, b_list gets changed as expected.
>>> put_map = map(b_list.__setitem__, idxs, ['YAY', 'YAY'])
>>> b_list
['a', 'b', 'c']
>>> list(put_map)
[None, None]
>>> b_list
['YAY', 'YAY', 'c']
Having said that, the proper way for get would be a list comprehension and for set a simple for loop. That also has the advantage that you do not have to repeat the value to put in place n times.
>>> for i in idxs: b_list[i] = "YAY"
>>> [b_list[i] for i in idxs]
['YAY', 'YAY']