BUG: Sparse structures don't fully support value assignment

[kernc]

Code Sample, a copy-pastable example if possible

>>> ss = pd.SparseSeries([1, 2])
>>> ss.iloc[0] = 3

-----------------------------------------------------------------------
TypeError: SparseArray does not support item assignment via setitem

Problem description

SparseSeries and SparseDataFrame don't support value assignment through some indexers (but might from others, i.e. ss[0] = 4 works).

Expected Output

Assignment works in all cases.

Output of pd.show_versions()

pandas 0.24.dev 5cb5880

[jorisvandenbossche]

The same is true for Series[sparse]:

In [44]: ss = pd.Series(pd.SparseArray([1, 2])) 
    ...: ss.iloc[0] = 3  
...
TypeError: SparseArray does not support item assignment via setitem