RecursionError raised on deepcopy of a sheet

[dsluo]

To reproduce:

Python 3.9.5 (default, May 11 2021, 08:20:37) 
[GCC 10.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from copy import deepcopy
>>> import pyexcel
>>> s = pyexcel.Sheet()
>>> deepcopy(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.9/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib/python3.9/copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib/python3.9/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib/python3.9/copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib/python3.9/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib/python3.9/copy.py", line 271, in _reconstruct
    if hasattr(y, '__setstate__'):
  File "/home/dsluo/thing/.venv/lib/python3.9/site-packages/pyexcel/internal/sheets/row.py", line 164, in __getattr__
    if attr not in self._ref.rownames:
  File "/home/dsluo/thing/.venv/lib/python3.9/site-packages/pyexcel/internal/sheets/row.py", line 164, in __getattr__
    if attr not in self._ref.rownames:
  File "/home/dsluo/thing/.venv/lib/python3.9/site-packages/pyexcel/internal/sheets/row.py", line 164, in __getattr__
    if attr not in self._ref.rownames:
  [Previous line repeated 989 more times]
RecursionError: maximum recursion depth exceeded

This came up during unit testing using Django's testing framework during the setUpTestData() phase.

[chfw]

wow! you hacked it!

I will provide a fix following this SO item