"TypeError: cannot deepcopy this pattern object" when there is a Widget with a compiled regular expression attribute

[int-ua]

Version: 1.0.1
Cause: #550

Widget:

class SpreadsheetPhoneFixWidget(Widget):
    def __init__(self):
        self.regexp = re.compile("^(\d{2})(\d{3})(\d{2})(\d{2})$")

    def clean(self, value, row=None):
        try:
            return "0" + " ".join(self.regexp.match(value).groups())
        except AttributeError:
            return value

Traceback:

Traceback (most recent call last):
  File ".../venv/lib/python3.5/site-packages/django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File ".../venv/lib/python3.5/site-packages/django/utils/decorators.py", line 110, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File ".../venv/lib/python3.5/site-packages/django/views/decorators/cache.py", line 57, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File ".../venv/lib/python3.5/site-packages/django/contrib/admin/sites.py", line 233, in inner
    return view(request, *args, **kwargs)
  File ".../venv/lib/python3.5/site-packages/import_export/admin.py", line 241, in import_action
    resource = self.get_import_resource_class()(**self.get_import_resource_kwargs(request, *args, **kwargs))
  File ".../venv/lib/python3.5/site-packages/import_export/resources.py", line 201, in __init__
    self.fields = deepcopy(self.fields)
  File "/usr/lib/python3.5/copy.py", line 182, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/lib/python3.5/copy.py", line 320, in _reconstruct
    value = deepcopy(value, memo)
  File "/usr/lib/python3.5/copy.py", line 182, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/lib/python3.5/copy.py", line 297, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib/python3.5/copy.py", line 155, in deepcopy
    y = copier(x, memo)
  File "/usr/lib/python3.5/copy.py", line 243, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib/python3.5/copy.py", line 182, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/lib/python3.5/copy.py", line 297, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib/python3.5/copy.py", line 155, in deepcopy
    y = copier(x, memo)
  File "/usr/lib/python3.5/copy.py", line 243, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib/python3.5/copy.py", line 166, in deepcopy
    y = copier(memo)

Workaround: do not compile regex patterns or move them out of Widgets.

[int-ua]

Should I add a test or will it be added to docs as a limitation?

[bmihelac]

Hi @int-ua, thanks for opening this issue.
I think that it cannot be fixed as deepcopy does not know how to copy compiled regexp. Django for example override deepcopy to avoid this on field validators. Having a note in Widget docstring should probably be enough?

[int-ua]

Yes, looks like a note would do, thank you. I'll close this if you don't mind, as this discussion must be relatively easy to find for those few who encounter this issue.