ImportError causing Exception while handling an Exception

[alexgurrola]

After a bit of debugging, I have narrowed the following error down to werkzeug/http.py#L26, which gives the following exception: ImportError: cannot import name 'parse_http_list'. Below is the entire traceback, which involves an exception inside the exception attempting to fallback to an old python reference.

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/werkzeug/http.py", line 26, in <module>
    from urllib2 import parse_http_list as _parse_list_header
ImportError: No module named 'urllib2'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "examples/http.py", line 2, in <module>
    from flask import Flask
  File "/usr/local/lib/python3.5/site-packages/flask/__init__.py", line 17, in <module>
    from werkzeug.exceptions import abort
  File "/usr/local/lib/python3.5/site-packages/werkzeug/__init__.py", line 152, in <module>
    __import__('werkzeug.exceptions')
  File "/usr/local/lib/python3.5/site-packages/werkzeug/exceptions.py", line 71, in <module>
    from werkzeug.wrappers import Response
  File "/usr/local/lib/python3.5/site-packages/werkzeug/wrappers.py", line 26, in <module>
    from werkzeug.http import HTTP_STATUS_CODES, \
  File "/usr/local/lib/python3.5/site-packages/werkzeug/http.py", line 28, in <module>
    from urllib.request import parse_http_list as _parse_list_header
  File "/usr/local/Cellar/python3/3.5.2_3/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 88, in <module>
    import http.client
  File "/Users/alexgurrola/Projects/intrepid/examples/http.py", line 2, in <module>
    from flask import Flask
ImportError: cannot import name 'Flask'

[davidism]

Please provide an example to reproduce this.

[alexgurrola]

Using Python 3.5.2 this paragraph in werkzeug/http.py will fail repeatedly.

try:
    from urllib.request import parse_http_list as _parse_list_header
    from urllib.parse import unquote_to_bytes as _unquote
except ImportError:  # pragma: no cover
    from urllib2 import parse_http_list as _parse_list_header, \
        unquote as _unquote

Also, the above script will complain on a deeper level without the try/except present, which alerted me to a possible change in the internal APIs with urllib. If it helps any, I found the issue originally when using Flask 0.12 and running the following script.

import os
from flask import Flask

app = Flask(__name__)
app.config.from_object(os.environ['APP_SETTINGS'])


@app.route('/')
def hello():
    return "Hello World!"


if __name__ == '__main__':
    app.run()

[untitaker]

Please rename your file from http.py to something else, otherwise it clashes with the http module from the stdlib.

[alexgurrola]

Apparently Python can't differentiate between scripts of the same name, so it sent me on a wild goose chase through these libraries... I appreciate the help.

[lby1992]

Please rename your file from http.py to something else, otherwise it clashes with the http module from the stdlib.

I'm new in Python, so I take the same mistake too....