BUG/ER: (GH2702) Bug with Series indexing not raising an error when the right-hand-side has an incorrect length

[jreback]

closes #2702

Base use cases (note that a completely changed series will morph to the new dtype if necessary)

In [1]: s = Series(list('abc'))
In [2]: s[0:3] = list(range(3))

In [3]: s
Out[3]: 
0    0
1    1
2    2
dtype: int64

In [4]: s = Series(list('abc'))

In [5]: s[0:2] = list(range(2))

In [6]: s
Out[6]: 
0    0
1    1
2    c
dtype: object

This is a bit odd, but allowed

In [4]: s[0] = list(range(10))

In [5]: s
Out[5]: 
0    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
1                                 b
2                                 c
dtype: object

These all will raise error messages now

In [1]: s = Series(list('abc'))

In [2]: s[0:3] = list(range(27))
ValueError: cannot set using a slice indexer with a different length than the value

In [3]: s[[0,1,2]] = list(range(27))
ValueError: cannot set using a list-like indexer with a different length than the value

In [4]: s[[0,1,2]] = list(range(2))
ValueError: cannot set using a list-like indexer with a different length than the value

With a step and a slice indexer (not sure was tested before)

When the length of the slicer matches exactly it works

In [5]: s = Series(list('abcdef'))

In [6]: s[0:4:2] = list(range(2))

In [7]: s
Out[7]: 
0    0
1    b
2    1
3    d
4    e
5    f
dtype: object

Raises when it doesn't

In [8]: s[0:4:2] = list(range(27))
ValueError: cannot set using a slice indexer with a different length than the value

[jreback]

@cpcloud @jtratner pls have a look when you can

[cpcloud]

Should there be tests for negative slices? Or are those somewhere else?

[jreback]

there are some in test_frame