Setting active sheet by Sheet instead of index

Created originally on Bitbucket by snorfalorpagus (Joshua Arnott)

The following syntax seems intuitive to me:

#!python
wb = openpyxl.Workbook()
sheet = wb.create_sheet("New Sheet")
wb.active = sheet

This code doesn't raise an exception, until wb.active is accessed again:

#!python
>>> wb.active
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:\Miniconda3\envs\python36\lib\site-packages\openpyxl\workbook\workbook.py", li
ne 134, in active
    return self._sheets[self._active_sheet_index]
TypeError: list indices must be integers or slices, not Worksheet

Instead we're required to pass the index:

wb.active = wb.get_index(sheet)

It seems like it should be easy to make the earlier code function as expected by automatically calling get_index if a Sheet is passed.