skip-existing option fails for new package

[mauritsvanrees]

If you call twine upload --skip-existing for a package that has not been registered yet, you get an error:

$ twine upload --skip-existing dist/maurits_cornice_swagger-0.3.tar.gz 
Uploading distributions to https://upload.pypi.org/legacy/
JSONDecodeError: Expecting value: line 2 column 1 (char 1)

This goes wrong in package_is_uploaded. The decode error is because we get html back that displays a 'not found' message. It tries to get this url:
https://pypi.python.org/pypi/maurits-cornice-swagger/json

Note that twine uses a url from the old pypi here, presumably because warehouse does not support this url yet.

This was discovered in zestsoftware/zest.releaser#191
For more information, see there. In that case, zest.releaser calls package_is_uploaded, which fails with this traceback:

  File "/opt/venvs/py3/lib/python3.5/site-packages/zest/releaser/release.py", line 198, in _retry_twine
    if repository.package_is_uploaded(package_file):
  File "/opt/venvs/py3/lib/python3.5/site-packages/twine/repository.py", line 176, in package_is_uploaded
    releases = response.json()['releases']
  File "/opt/venvs/py3/lib/python3.5/site-packages/requests/models.py", line 826, in json
    return complexjson.loads(self.text, **kwargs)
  File "/opt/venvs/py3/lib/python3.5/site-packages/simplejson/__init__.py", line 516, in loads
    return _default_decoder.decode(s)
  File "/opt/venvs/py3/lib/python3.5/site-packages/simplejson/decoder.py", line 374, in decode
    obj, end = self.raw_decode(s)
  File "/opt/venvs/py3/lib/python3.5/site-packages/simplejson/decoder.py", line 404, in raw_decode
    return self.scan_once(s, idx=_w(s, idx).end())
simplejson.scanner.JSONDecodeError: Expecting value: line 2 column 1 (char 1)

[sigmavirus24]

Excellent catch!

[ofek]

Scratch that, pip didn't give me latest. All is well.