Response allows invalid status

[RazerM]

I was accidentally passing a string status like '200' from Flask.

>>> from werkzeug import Response
>>> Response(status='200').status
'200'

This status isn't valid according to PEP 3333 and e.g. breaks Twisted's WSGI runner. Obviously the error was mine, but I thought perhaps Werkzeug should raise an error earlier.

Werkzeug already does some validation or coercion into the correct format:

>>> Response(status='abc').status
'0 abc'
>>> Response(status='').status
Traceback (most recent call last):
  File "/Users/frazer/.pyenv/versions/venv/lib/python3.7/site-packages/werkzeug/wrappers/base_response.py", line 314, in _set_status
    self._status_code = int(self._status.split(None, 1)[0])
IndexError: list index out of range

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/frazer/.pyenv/versions/venv/lib/python3.7/site-packages/werkzeug/wrappers/base_response.py", line 202, in __init__
    self.status = status
  File "/Users/frazer/.pyenv/versions/venv/lib/python3.7/site-packages/werkzeug/wrappers/base_response.py", line 319, in _set_status
    raise ValueError("Empty status argument")
ValueError: Empty status argument

status only becomes invalid if both of these conditions are met:

1. int(status) doesn't raise
2. len(status.split(None, 1)) == 1

The current implementation:

werkzeug/src/werkzeug/wrappers/base_response.py

Lines 307 to 320 in e7ba08f

	@status.setter
	def status(self, value):
	try:
	self._status = to_native(value)
	except AttributeError:
	raise TypeError("Invalid status argument")
	try:
	self._status_code = int(self._status.split(None, 1)[0])
	except ValueError:
	self._status_code = 0
	self._status = "0 %s" % self._status
	except IndexError:
	raise ValueError("Empty status argument")

If line 315 used the property setter instead (self.status_code = ), the result would be valid:

>>> Response(status='200').status
'200 OK'